Epic roadtrip

My friend and I live in Copenhagen in Denmark and are going on an epic 6 month road trip around the United States. We are looking for a minivan that we can take the seats out of or a small truck with a bed topper so we can sleep in the vehicle. We are students on a limited budget and want a vehicle that we can sleep in, gets ok millage and that is reliable. Just looking for suggestions about what we should look for when we arrive in a few months. Thanks. S and T