Buying a used van: what to look for

Just wanted to come back and update....we bought a van today! It's a e350 with a v10, just like you guys told me to get :). 2003, but with lowish miles (125,000). It looks like someone probably used it for exactly what we want to--a tow vehicle for family road trips; it has 4 captains chairs plus a 3 seat bench (only part I'm not crazy about....it means we can only fit one extra person if the kids want to bring friends along on trips), plus they added a dvd player, bluetooth and usb ports, navigation system, etc. I think the kids are probably going to balk at having to ride in my minivan instead of the new van day to day ;).

So now we just have to find a trailer, which should be the fun part, right? Thanks again to everyone for all the help!