60 mph on the highway in an RV? I think I saw you recently. There were 40 cars lined up behind you, half of them trying to get to work and becoming enraged. You may be retired and not in a hurry to get anywhere, but the rest of us are not. Show some consideration for the rest of us. Make saving a life more important than saving a gallon. Keep up with the flow.
If you cannot keep up with traffic and still get the mileage you desire, perhaps you should get a smaller RV. Meanwhile, stay off the highways.
I don't mean to seem rude, but the attitude of "I'm in no hurry, so how slow should I go with my RV" needs to be challanged. It's downright dangerous.