Acei -
You can purchase a dual-fuel or a tri-fuel Honda or Yamaha inverter type generator pre-converted, or convert after you get the (gasoline only) gen.
IMO - either one is a better choice than Onan.
See: Central Maine Diesel -
Central Maine Dieseland US Carb. -
US Carburetion, Inc.BTW - you can also convert the off-brand (Chinese knock-offs) - either the inverter type or non-synchronous (constant rpm) generators.
Also - some of "us" prefer to have our generator in the truck bed - rather than in the 5th itself.
Another option is to order a 5th with "generator prep" - but not the generator.
Dealers gouge you for the gen - and don't give you many -or any- options.
Decide what you like/want (or need) - and add it later.
How much generator do you need if you're using electrical hookups at campgrounds -or- solar if you're boondocking?
Forget diesel. Works real well for diesel pushers (gen is in front) -and- they (DPs) are on a *very* substantial chassis.
Knew a guy who had a *heavy* water cooled, well insulated (quiet) gen permanently mounted behind the cab of his MDT (and towed a 5th).
Only reason he had it - was he fell into a "deal". A guy bought a 'dressing room' travel trailer from the studios. Rarely moved - gen was mounted on the tongue. No propane tanks.
New owner didn't want the gen on the tongue of the TT (can't understand why, LOL!) - nor did he have any place for usage.
So, he sold the gen dirt cheap! The friend couldn't resist a genuine bargain - and it was just a flea on the back of his MDT.
Happy voltage for your voyages..:B
~