Given what you've said so far, I would only consider 2500 or 3500 SRW and likely in diesel. You are guessing the TT weight to be around 6000 dry and 8000 ready to travel I don't know if you are including the weight of your generator, solar, and batteries in the dry weight estimate or not, but if not, you will be hard pressed to be at or under 8000. 9000-10000 Wouldn't surprise me in the least.
The payload of the F150 Supercrew with a short bed and 3.5 Ecoboost is around 2100 if I recall correctly. Depending on exactly how the layout of the TT is, you may end up with 1000+ tongue weight and will certainly have more than that with the WD hitch included. You said you are adding an in-bed tank so that will add another 80-100 lbs for the tank and then the weight of the fuel at 6 lbs/gallon for gas. So even a 36 gallon tank will add around 300 lbs with fuel. I think you run out of payload by the time you add people and stuff now assuming the tongue weight isn't higher than estimated or you aren't getting a bigger auxiliary tank.
Get the 3500 SRW and don't worry about it anymore (at least that is what I would do)
