"heavy load" connected to outdoor GFI receptacle fed from another
outdoor receptacle via zip-cord? Really? Why not put in some proper
wiring, fastened with screw-terminals or anything better than what you
get with a plug/outlet? Wiring suitable for environment.

Most aspects of electrical code have to do with fire prevention, and it
sounds like you're heading the other way.

Are you devising this on your own? I'd suggest you consult a local
electrician for tips.

J