Seriously? You need 20 amps while boondocking? IMO, you need to decrease your power needs... Otherwise you'll find your batteries don't last long and you have to make noise (generator).
I'd recommend reducing your power needs (drastically), and second the recommendation of getting a true sine wave inverter. They cost more, but you'll have fewer issues with noise in electronics and everything running off of it will run more efficiently.
Don Rowe (link posted above) is a good resource, and a good place to buy.