Just do it right the first time and be done with it. Have a 30 amp 120 volt breaker installed in your panel and run a dedicated line out to a wall where your rig is parked, install an outdoor box with the proper outlet and your done. I did my own and cost was under 100 bucks, and that is what a good 10 gauge 50 foot extension cord will cost you.
Doesn't matter what size, gauge, or length extension cord you use, your still going to trip breakers when you start turning on stuff, maybe not just one item, but when you start turning on lights, or something in your garage, it will start tripping breakers.
By the time you've bought extension cords and adapters, you will have spent enough to do it properly.