OP,
We decided on a 5th wheel for retirement due to $. In our many years of calculations, a 5th wheel and truck are less expensive to maintain and insure. We have owned Class A's, Class C's, Diesel Pushers and 5th wheels.
With a motorhome and tow car, you have two motorized vehicles to maintain and insure.
For 60-70k, you can get a really nice truck/ 5th wheel set up. That kind of money spent on a motorhome will not get you too much these days, and buying used is tough. You never know how well the RV was maintained.
If expense were not an issue for us, when we begin full timing next year, we would much rather have a DP. Easier to park, level, go use the potty, stretch your legs, change drivers, make a sandwich, etc. Our last 39 ft DP didn't seem to have near as much room as our first little 26ft POJ 5th wheel we bought.
Gas mileage is not really a factor. We think they pretty much even out either way.
Only you can decide what is right for your situation.
Best of luck.
