So, what size Gen-Set will you need built into this trailer?

let's conservatively estimate that you need 50 bhp at the vehicle engine to give "reasonable" performance (That's about the same as an old air-cooled rear-engined VW 1600cc, running flat-out, or about 1/3 of a modern car engine)

Each bhp is about 750W, so you're talking 37.5 kW. If you run that at 12Volts, that's 3,000 Amps. You can do some serious welding with that! of course, you can step-up the voltage to 110V at "only" 300 Amps, or get a "safe" Amperage with 10 KV!

Caterpiller do an 18 kW diesel unit. it weighs 1000lb. You would need two of these. So by the time you've got it in a trailer, added a fuel tank, and made it road-legal and accident safe, you'd be towing a 1-ton trailer.

You wouldn't go up hills very well with 50 bhp, or accelerate very well at all.

Diesel-electric drive is great in large prime-movers like Locomotives, ships, tanks. It sucks in a family car...