I have a 2008 AWD Highlander with over 100K miles on the odometer. Roughly 85,000 of those miles have been put on with a 16' or 17' trailer in tow. Mostly a cargo trailer (6x12 box, with tongue it's 16' long, weight
about 3500 lbs). But also have towed a 17' 2300 lb. Burro
and a 16' 2700 lb. boxy KZ Escape
travel trailer for thousands of miles each. Through all this the Highlander has towed admirably with no mechanical or handling issues.
You should be fine towing a 16 Casita. A 17' won't have much different aerodynamics but its tongue weight
can be substantially higher, maybe too much for the Highlander's rear springs. That would be my only reservation.
The Highlander's brakes
are great. Add a trailer with its own brakes
, and you have plenty of stopping power.