Those who have waded through my posts of the past will know what I am about to say... the Toyota Sienna
works very well for towing, at least for a trailer the size of my 17' Boler
(wider and slightly heavier than a Scamp
16'). Compared to the Highlander, it has more wheelbase (which is good), and essentially the same drivetrain (which is more than adequate, in my opinion).
If you are going to a van
and want all-wheel-drive, the Sienna is an option, and there are likely others (I'm not sure which ones in this model year). Most rear-drive vans are much larger (and heavier) than a "minivan" such as the Sienna; the exceptions would be the Chevrolet Astro (if you can still get one), and the Dodge Sprinter (large but lean).
As for the Highlander
The maximum tongue weight
should not be a rumour, and I don't trust dealers for technical information. My manual explicitly provides the maximum hitch weight
, both without a weight-distributing hitch (350 lb) and with one (maybe 450 lb, but I don't have a WDH so I don't remember). The towing section of Toyota manuals can be hard to read because it is so wordy, but I suggest another look.
While the Highlander does share drivetrains with the Camry (and Sienna, and Lexus RX), and probably steering and front suspension as well, I believe that it has its own unique rear suspension
. Whether shared or not, if the only concern is a lack of spring stiffness (not load capacity), then air bags may be the solution - I added Firestone Coil-Rite bags to my Sienna, and am very satisfied with the result. They correct the ride height and add stiffness, but only when you want it for towing and pump them up.