Once upon a time.I had a realy nice genbox on the rear of my TT.
I carries a 4300 watt Robin Subaru genset in an aluminum fan cooled genbox
It worked well and never had any issues.
However it did impact the handling of my combo simply because between the rack, reinforcing the rear and the genset itself, I added a lot of weight behind the axles.
The rear genset was not push button convenient , I had to manually plug in but that could have been resolved with a transfer switch, remote start and more wiring. I still had to deal with gas cans and transporting gas.
While I did enjoy my rear mounted genset, built in is a better way to go if for no other reason than to avoid the weight in-balance and pin weight issues.
Between the axles will always be more stable than behind the axles.