..First off, see the picture in my signature, for an example that sums up IMO the best way (and only way I would) tow with a minivan, haha. :)
I have to agree with the previous suggestions about a full size conversion van. That would work muuuuuuch better for what you want. If we ever go back to towing an RV trailer with the family, that is what I'd get.
Best case would be if you could find a standard length (not extended) Ford E-350 van with the V10 engine. Reality is, as already said, E350s like that are not easy to find. I'd definitely try to find a standard length one. The extended ones are bigger inside, but not quite as stable for towing. For what you want to do, the V8 engine would work also if you can't find one with the V10.