Ok now I'm livin your dream with you!! Lol
Transfer Tank in the TT is another good idea.
Also check out JME or rds tanks online. You can get a 51 gal slip tank that is only 9" wide. These outfits will fab what you want too for not a lot extra. Looked into it with JME but ended up finding a stock tank that would work.
Definitely get a long bed. Don't even try to cram all this in a short box truck.
My aversion to this is I would not want to haul AND tow a heavy load at the same time and still try to enjoy the scenery! But if you got a TC its a wind break and the trailer is kind of along for the ride. I've pulled a 6-7klb trailer behind the TC and given the weight and wind resistance of the TC, the trailer was not very significant. With an 8' lighter weight camper, even with a slip tank you could pull without a hitch extension.
Also after traveling extensively in AK with a diesel/TC, even there you still don't really have to worry about fuel unless you're going off the grid for long periods, weeks.
Especially if you got a bigger replacement tank for the truck.
Diesel generator is a solid idea for home base. Think about the weight though. I hate built in generators as you can always hear and feel them while in the camper and wheeling a big generator around is a chore and dunno where you'd store it unless you got a toyhauler TT.
IMO use propane for where it is intended. Having self contained TC that you can keep the fridge in propane while underway is invaluable. 2 - 6V batteries, solar and a little Honda genny is all you need for a TC. Unless you're intent on performing every power sucking activity simultaneously.