Which side should rough wiring for roof ac be on?

Good to know solid wire should not crack. Maybe I was mis-informed, or have dated info. I have never seen cracked wire either.
Despite any code, I would not think a heavy extension cord would be more fragile than a solid wire clanking around inside an RV wall. Im not sure what the issue would be,
but it will be a lot cheaper to use house wire than expensive stranded wire…