You guys are getting terrific milage out of your DP's. I would have to contribute that to your driving. I sell RV's in Central Fl. and we specialize in diesels, Newmar, Holiday Rambler (Monaco). For gas, I would suggest National RV.,(Seabreeze, Dolphin) because of their steel structure. You must reinforce the frame rails if you are going to tow a heavy load on a gas coach, re: racecar, you'd be surprised at the bent frames and floors I've seen over the years.
The diesel class C's haven't been too succesful because of the noise factor, (18 inches inside) and added weight. As in racing, safety is a must. If I can help in anyway, let me know. Don't forget, like a Ferrari, once you buy it, now you must own it ($$$$$), they are wonderful to have at the track and vacations, but can be expensive to maintain.
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