First off, test drive a gas motor home, and then a diesel.........you'll see the difference. Make sure your test drive includes freeway driving so you can feel how they handle when a big rig passes you. Try driving up a long grade so you can compare power, plus the noise difference between a gas rig when it down shifts and revs up........typically you can't carry on a conversation because of the noise. Right now diesel is about a buck and a half more here in California the gas, so that's a consideration Both Gas and Diesel will get about the same mileage, which is around 8 mpg. I've had 3 gas motorhomes and 3 diesel pushers. Make sure you look hard at the floorplan. One of my diesel motor homes, didn't have any place to put a garbage can under the sink, also the sink in the bathroom, had barely enough room for a tooth brush. Spend some time sitting in it and just looking around for awhile, to visualize what it would be like to stay in it from a comfort level. Typically gas motorhomes are less expensive to maintain then diesels......oil changes are less, tires depending on the years, are bigger then gas, hence cost more. One other thing, if you're looking at older Monaco, stay away from the R4R Chasis........they ride terrible. The R4R's were found on the low end of the diesel line for Monaco, Holiday Rambler and Safari's. Again, test drive over serveral different roads to see how they handle and ride.........Don't be afraid to take it out for 30 or 40 miles test drives, it's one of the best things you can do when thinking of buying.