Thinking About a TT, Confused About Towing

Here's our real world experience towing with a V6 4Runner: 2008 vehicle pulling a 2009 single axle Bigfoot fiberglass trailer. Trailer is 20 ft total length, 4200 lbs loaded and weighed, 500 to 550 lb tongue wt (about 13%). We use the WB hitch that came on the car and are right at recommended max for tongue wt and rear axle GAWR. I was concerned about this, but the trailer tows beautifully. No sway even with trucks or crosswinds. Trailer is 9 ft high by 8 ft wide, so not as high as many, and has a lower center of gravity. We're careful how much stuff we take along to stay within the payload of about 1250 lbs. I inflate the rear tires to about 42 psi to give the same footprint they would have without trailer and 32 psi. No unusual tire wear, original P rated tires. We tow with empty tanks except for water heater, about 50 lbs. We've been from Portland to Jasper twice and to Montana two other times. I-90 through Idaho had us down to 30 mph but otherwise we do ok. Headwinds are murder. With no winds, 14 mpg. Drive about 60 mph. Drive in D mostly but use the shifter on hills, in winds, etc. I drove stick shifts for 40 years so using the shifter makes sense. I tried air bags in the rear springs but after eight trips back for leak repairs, I took them out and now use Timbren rubber axle bumpers. We never feel bottoming. I think the Timbrens are probably on the axles all the time, unlike the original jounce bumpers inside the springs. We have about 15000 miles on this combination and usually carry a big 20 ft kayak on the roof and sometimes bikes in the car. This is the max a V6 4Runner can pull, IMO, but a Casita or Scamp would be an easy tow.