While my normal extension is a 75' 14 gauge for keeping batteries changed and running some 120v items, I have a 50' 12 gauge that just reaches with my 30 amp cable fully extended and I use that if we get somewhat rare hot muggy weather in Vermont so I can run the AC since the house doesn't have AC. Then we camp in the driveway in cool comfort.
2015 F350 XLT PSD CCSB SRW, Andersen Ultimate hitch
'12 Cougar High Country 299RKS, Mor/Ryde Pinbox
1/77 Armor Bn, 5th Mech, I Corps