I agree that it will be hard, if not impossible to sell in the USA. Don't let that get you down. There are still options for you. As someone else mentioned you could swap/trade with an American looking to do the same thing in Spain.
I met a couple from Germany this weekend. They were buying a motorhome here in the states and plan to use it for 3 years as they tour our country. Then they will sell it and go home. The way they figured it out it was the least costly way for them to spend a few years here in the USA while getting the see all of the USA. It sounds like a great adventure. The only problem is that they bought the motorhome I wanted. We ended up getting, what we hope is, a great one but it cost me more money.