I WOULD HAVE RECOMENDED TO BILL THAT HE JUST BUY A CLOTHES-PIN FOR HIS NOSE. WHEN USING THE OLD FISHING CAR. THAT WASHING IN A CARWASH IS REALLY BAD AND THOSE THINGS THAT COVER-UP THE SMELL ARE ONLY TEMPORARY.
I would worry that if you went to the car wash and sprayed out the car, in addition to all the other stuff you’d have a car infused with mold.
I’d try to clean off the guano, and if it would be too much work to get it all, and this is your backwoods utility car, why not just rip the dash board (or at least the cover and anything with guano on it) and junk it. Maybe put in a nice wood one or something 
Besides cleaning the car out, I would try using a product calls Smells Begone. I got it at a local hardware store and it really did a good job of covering the odor of a dead animal behind my heat pump that was stinking up the entire upstairs of my house.