A couple of things.
The Astro was a marginal tow vehicle at best. I owned one, I know. I loved it, but it wasn't even good for towing a large pop-up. By today's standards the Astro is a lousy tow vehicle.
The Astro is a uni-body with a frame bolted on for extra rigidity.
Astro: 190 HP @ 4,400 rpm; 250 ft lb @ 2,800 rpm
Highlander V6: 270 hp @ 6200 rpm; 248 ft-lbs. @ 4700 rpm
The Highlander with the V6 will probably out tow the Astro. More HP, and longer HP and torque curves. Don't bother with the hybrid. It's stunted for mileage, so while you might be able to tow with it, I don't see that as being a pleasant experience.
Towing a travel trailer ain't cheap. Yes, you can tow up to your capacity, you will be safe, and people will tell it's no problem. However, I can tell you from experience (I towed two trailers at close to capacity with two different tow vehicles) that it's far easier and more pleasant to tow with a vehicle that is properly sized for your trailer, and has a reasonable amount of reserve capacity.