An RV power cord, is usually rated at a minimum of 30A, usually 10 gauge
Your house supply won't provide more than 15 or 20,, but I would be inclined to go for the full 10g, combined with a good quality adaptor to let you plug it into the house outlet. That way, you've got a nice long 30A cord that you can take with you, when you do get to travel.
That's quite a long cable run, and anything smaller will give you a significant volt drop. This may also give you issues with an electrical protection unit, if you have one.
Try to connect to an outlet that doesn't share a breaker with anything else, because you'll be pushing the limit of a domestic 20A supply with your AC.
IanP, the man from Scotland
Jay Feather 19XUD, pushing a Jeep Grand Cherokee