[scottz]

I don't know about your Onan 6500, but my 5500 has a 30A breaker on each output leg.

A 5.5kw generator would max at 46A (5500W/120V), or 23A on each leg; so the 30A breakers are sufficient. A 6.5K generator would max at 54A, or 27A on each leg; it will probably also have 30A breakers

In case you are wondering about the ability of your generator vs shore power:

50A Shore power
2 legs @ 50A each provide 12kw to the trailer (50x120x2)

Generator
2 legs @30A each could provide 7.2kw to the trailer (30x120x2), but my generator is limited to 5.5kw. Yours will be 6.5kw.

30A Shore power (not a Montana)
1 leg @ 30A provides 3.6kw to the trailer.

Bottom line; a 5.5KW provides about half the power that the 50A shore connection provides but a lot more than a trailer with 30A shore power. I have run both AC units with my generator, but can't remember running the microwave at the same time; it probably would not handle that.

As for your wiring question: you only need four wires. Hot 1, Hot 2, Neutral, Ground.

Here is a picture of my generator junction box and the transfer switch wiring schematic.