Hello! Short to ground?

Stardog wrote:
Unfortunately even with everything turned of in the RV we trip the GFCI in the garage outlet that we plug it in to every time.

What should the resistance be between the prongs on the side of the RV where the chord plugs in?

First, a tripped GFI is not the same as a tripped breaker.
It is caused by a LEAK to ground.

Start by turning all of the AC breakers OFF.
If it does not hold then, you might have a bad GFI outlet.
Try plugging into a different outlet.

The resistance you ask about is impossible to determine. Too many variables. But with all the breakers turned ON it might be really low.

Edit: I see that that's all been tried......so it appears that you have a ground fault at the input point OR between there and the breaker box. OR there is a "branch" feed that goes to breakers elsewhere or the branch circuit doesn't have a breaker.