My first two rigs were gas - our third is a DP (as noted in my sig below)- once you go DP, you never go back!. The difference is like plain biscuits vs Double Chocolate Cake!!
My personal experience: a gasser needs more regular maintenance and the engine components are subject to more frequent failure / replacement (starter, generator,belts, etc) as gassers are mostly built on lighter frames.
A DP is usually built on a heavy-duty truck or bus chassis and the whole complex is much more robust - but the regular maintenance is still a MUST!! Oil change on a gasser at 6 months - about $50. Oil change on my DP each year - $250. (Shop rates are over $110 hour here, so labor is a big part of the cost - if you can DIY, the cost is MUCH less! (But at 79 years, I am happy to pay the labor cost.)
If you would like an extensive pre-purchase checklist for a DP, just send me a PM - I have a couple that may be of use to you.