Gas vehicles 'sit' better than diesels. If you can take it out at least once every 2 months, this may not be a critical factor. At least when towing, on uphills, diesel outperforms gas (Power Pack may compensate, though). On downhills too I think, due to the availability of 'exhaust braking'.
And a diesel in back with generator in front seems to be a more conveniant layout (engine far from driver and generator far from sleepers, and no hump for the driver to get around). Diesel engines seem to be much longer lived than gas.
Oil changes for a diesel are more exciting - gallons rather than quarts Each fuel has problems in storage - gas breaks down and can clog things up, while diesel has problems with water condensing in it and even a bacteria which likes to grow in it. Plus diesel 'gels' in cold weather.