Walmart sells RV extension cords (as does any local RV dealer). Using just 30 amp cords, 40 feet would not be a problem. A good dog-bone 15 to 30 amp adapter is better than the little round junk jobs.
Your A/C is kicking out on overload due to low voltage. Since you're not tripping your house CB the problem is length and size of the cords.
A meter to check the voltage in the house and RV would be a great help in finding out what the problems are.
If your reefer is on, it can be drawing 350 watts, and converter could be drawing up to a few hundred watts. If you want to run the A/C turn off everything else in the unit to keep load as low as possible.
A 30 amp dedicated circuit would be nice, you could plug in without any trouble, but running just the A/C should not be a problem.
Doug
