thanks all for your comments.
Avoid driving into headwinds, hold your speed to 55 mph, limit A/C usage…But AT BEST that will only give you an extra 2 mpg…If we bomb Iran, you can scrap your motor-home or find “the best spot” and leave it there…
I’m going to disagree with most and say that aerodynamics are so important, that dropping your speed to the 55 mph and below range would definitely help. Eliminating all excess weight helps too. Having said that, I am doing a complete turnabout and say, your first responsibility is to your fellow drivers and keeping up with the flow of traffic, and generally maintaining a speed close to the limit, one side or another.
Generally, we should reconsider any driving technique that may help mileage, but puts others and yourself at risk…like allowing your speed to build up too much going down steep inclines.
On the tail end of dagosa’s thought, here’s a way to find some folks who are serious about aerodynamics: http://ecomodder.com/
Personally, if you could keep it safe and legal, I’d get a kick out of seeing some experimental aero-mods to a motorhome.
Absolutely aerodynamics are important. The problem here is the scope of changes needed to make a difference on an RV. One had better be very good at attaching the large modifications needed, the forces on them are much greater than what a small car’s spoiler would be.
And I agree with Dag, while slowing down improves mpgs the rolling traffic barrier that results is not safe, especially on a 2-lane road.
Cig…"Prototype aerodynamic boat tail good for +15% MPG boost"
As an avid sailor, this caught my eye. The drag created in the back is at least as if not more important for some vehicles and am wondering what there is out there (smaller of course) that could inconspicuously be hung on the back (and including wheel skirts),on the cheap of course. Air tabs ? http://www.sti.nasa.gov/tto/Spinoff2008/t_3.html
Its probably not all that hard to accomplish this stuff. (e.g. here’s a boat tail for a box trailer: http://www.greencarcongress.com/2005/11/new_boat_tail_d.html There also have to be reasonable underbody mods that can be done. I’ve seen a lot more of these lately: http://www.vehicleservicepros.com/article/10262319/are-trailer-side-skirts-in-your-future)
Its just not been anyone’s priority. And then, if you started really doing crazy stuff like this to cars you’d have a hard time selling them since a lot of it looks odd.
I keep having this fantasy that one day my life will have “spare time” and I am going to start a couple of projects mostly for fun and curiosity. One will be simple aero mods like internal side mirrors, wheel well covers, some kind of rear mod for drag…stuff like that. But I like to tinker.
Can you say “Diesel Pusher”??
A senior citizen on a fixed income probably isn’t looking to spend $100,000+ in order to gain 3mpg. 
This discussion has been great and really has exceeded my expectations of coming up with good ideas. The aero mods mentioned by Cigroller, Dagosa are definatly something I plan to explore further.
Like cigroller, I like to tinker and I get alot of joy and satisfaction at looking at problems and experimenting with pragmatic solutions. My reality is that I have limited funds and a 15 year old RV that I have driven for 120K miles. The RV is in like-new condition, runs perfectly and I take alot of pride in keeping it well maintained but it still a “rolling brick” with little value to anyone but my wife and me. I don’t expect to ever be able to afford newer one or a diesel pusher so I am searching for practical ways to improve the mileage, allowing me to continue to RV in the most cost effective manner.
btw…Safety and consideration for others has always been and will continue to be my main concern. I make it a practice to use “pull offs” to allow traffic to get by me whenever I can. While I am a senior citizen at 67, I am not a Sunday driver.
One other thing - are they coming out with ‘low rolling resistance’ tires for RVs? Next time you need them it might be worth a look. The Michelin web site lists several.
Here’s a no-kidding way to get over 25 mpg from your RV system (it worked for us for 1-1/2 years).
Buy a good towed car.
We had a Ranger 4 cylinder stick that was far more practical to drive than the RV for shopping, sight-seeing, general traveling, etc. We put three or four times the mileage on the Ranger that we did on the RV. You can find plenty of good advice, many manufacturers make tow systems, and a towed car will increase the level of good experiences you will have on the road, too, amigo. When you are done with your travels you will also have a decent vehicle. Of course, check the weights and allowances for your RV to see ensure you are within specs with the vehicle’s tow weight. Good luck!
Satificer makes a good point. With 120k (that’s a ton on a RV) I would guess at a minimum your trans us getting tired, since you can’t afford a new RV. I would keep my eyes open for a cheap dsl re-power. Start looking for a wrecked van with the powerstroke, buy the whole thing as you will need lots of parts. then one day swap drive lines, not an easy job but long long run a good option.
HHHMMMmmmmmm…Well okay…Find a 30 or 40 footer parked in a sweet spot with a blown motor or transmission, buy it for salvage and settle down…Why keep looking for Nirvana once you have found it…Especially at $4-$5 a gallon…
Thanks all for your interest and great advice. Take care and I’ll see you on the road…
Minnemike, since you indicate that you get a lot of joy and satisfaction from looking at problems and experimenting with pragmatic solutions. and you have the luxury of time, allow me to suggest something unusual.
Creating a fiberglass modification (attachable) isn’t as difficult as many think. It consists primarily of creating framework of wood, creating the form of wood strips laid over the framework, smoothing the shape with sanding and glazing compound, then coating that with a release and using that to make a mold. The mold is then cleaned up and fiberglass resin with the glass cloth is laid in. A much better end iten can be obtained by allowing a coat or two of plain resin to cure then adding layers with glass cloth behind them. I’m sure the bookstore has a good book on these precesses. It’s even possible that coating the inside of the mold with epoxy based paint (such as that used to refinish bathtubs, available at any hardware store) could creat a part with the color right in the fuberglass. That’s basically what boat manufacturers do.
In ahort, you could creat your own boattail or bobbed rearend.
“In short, you could creat your own boattail or bobbed rear end.”
I don’t think that this is practical. The boattail would have to very long to be useful, and the RV is long enough already. It seems to me that it would have to be at least 10 feet long; probably more. It could be a fun project to check into the physical requirements, though.
That’s what I was thinking, JTS, not like an RV is compact or anything…
Also, the abrupt flat/square rear end of an RV is actually not bad, they called that a ‘Kammback’ on cars, aerodynamically efficient.
I agree with the OP’er that reducing road speed is going to give the most bang for the buck. From what I recall, wind drag goes as approximately the square of the speed, so if you reduce speed by 1/2, you reduce wind drag to 1/4 what it was at the orignal speed. I’m not suggeting the OP mosey down the freeway at 30 mph, but even reducing the speed from 60 to 50 should result in an appreciable increase in fuel mileage.
\There’s an article in the current issue of Popular Mechanics about this subject for those interested.
The other problem with creating the rear aero-cone is that you’re going to have an awful lot of vehicle behind the rear wheels, which means the back end is going to swing wide when you go around corners. That’s a good way to take out a gas pump or the guy in the next lane if you’re not careful.