25' 30 amp extension cord

I agree, the quality/durability of extension cords is usually in the insulation, the connectors, and the wire stranding. (flexibility) I like Hubbell connectors. They are generally industrial grade, have hundreds of options for most every application and they are replaceable should you overheat a connector due to overload or a bad receptacle on someone else's part. You can repair/fabricate your own cord of any length should you not find one to your liking. Thick quality copper cable has high scrap value and a tendency to walk off if you aren't careful.

Chum lee