I know there are a number of folks on here towing campers with their Sienna. Since we're all about lightweight towing, I thought I'd post a link to a forum I run: http://www.lightweightcamperforum.com/
The forum was spawned out of a request from people on the Yahoo FunFinder group, and I expanded the idea to include ALL lightweight campers. We've got various members who tow anything from pop-ups to small hard sided, to fiberglass "eggs". Hope some of you with an interest will come check it out!