I would think that a 40 A main with a two pole 30 A GFCI and two or four single pole 20 A GFCI would be a better choice.
With a 30 A main and a 30 A GFCI, when fully loading the GFCI, you are in a race between both of the 30 A breakers.
Having two or four single pole breakers allows you to use mutiple small loads without one breaker trip making everything stop.
How do you deal with grounds and neutrals? Is the centertap of the generator windings tied to the generator frame? Is the generator frame bonded to the trailer frame? Do you drive ground rods or drag chains?
What does MSA state about temporary portable power for strip mines?
