The Astro van tows my little camper great, and has plenty of interior room in it. I'm a big fan of full-frame RWD vehicles, and if it was my choice, I'd be getting a Tacoma, 4-runner, or one of the new Chevy Colorados. The wife though doesn't like vehicles that feel "big", and likes the softer, more car-like feel of a unibody vehicle, and the rack & pinion steering. The Astro quite a solid vehicle, and that's why I'm reluctant to replace it, but I am hoping the benefits of modern technology though can gain us some in fuel mileage both on road trips with the travel trailer, and around town... just can't afford to have a separate vehicle sitting around just for the use of taking the occasional road trip with the TT, so if we replace, we will need to get a multi-use vehicle.
My company had a few of the Freestar cargo vans. They handled pretty good with the low center of gravity. Never towed with them, but they did haul lots of flat-panel TV's, PA speakers and other heavy audiovisual gear. All of them however had the transmission grenade on them at around 220K to 250K . Was unfortunate, because they all had great engines and chassis in them when the transmissions failed. Never towed with one though. They have great payload capacity I'd be worried about the back end squatting down a little too much with a high tongue weight, as it's already rather low to begin with. Highlander has a pretty high profile suspension, so this doesn't look to be too big a deal with those.