Seems like a couple OP's have your wire sourced, so I'll just add that Marine wire has the copper strands protected by Tinning, useful in that exposed are of your RV chassis.
And, let me mention something a good RV parts & repair shop (Karen's in Anchorage) told me: Don't use the axles as conduit for the wire. They rust inside and the rust abrades the insulation. Better to band the wire TO the outside of the axles. From my experience on boat trailers, Black Plastic Electrical Tape holds up longer than ZIP Ties.
Marine wire has the copper strands protected by Tinning, useful in that exposed are of your RV chassis...
My family used Karen's. I have used Mobile Trailer (also in ANC) and been very pleased with them. Both are on the North end of town, near the rail yards.