Ideas for carrying/securing open framed generator

I keep my 3400 inverter in my truck bed, tied to a brace, if needed i would have a welder make a bracket to connect it to my TT bumper.

you have stated about 500, but thats with the trailer still being empty,
Do you intend to carry other weights in the front parts of the trailer, advertised weights sometimes dont count propane or tank weight, nor do they count battery weight, frequently water and waste tank weights will be on the tongue, at least in part. All that weight counts.