Definitely mirrors. (I'm not sure the best sort for a TB. I've never had one.)
Good quality WD/sway control hitch. E.g. Equilizer, ProPride, Hensley. There are some others similar to the Equilizer.
I also liked the gizmos. I didn't have AC on my old hybrid, but found the gizmos very useful in cold weather camping.
My old Hybrid was a 2008 RVision TrailSport 21 RBH. It weighed 3400 fully loaded (measured at a CAT scale, disconnected from TV - I did things to make it lighter, like removing the AC) and had a ludicrous 6000 lb GVWR. I towed it with an '08 Toyota Sienna for 8 years (same car I still use) - from the Black Hills to Massachusetts, Ontario, Florida, etc... At least once a year, across I-68 through WV and Maryland to Delaware (7 and 8% grades). Never had any issues. Don't be in a hurry, learn your car's engine, transmission, and power band. Don't be afraid to use them. To go up grades, put the engine into the power band (engines produce the most power within a certain range of RPMs - this varies by engine type - Toyota's 6 in the Sienna is best at around 3400-3600 RPMs so whines like a mother, but can really haul) and hold it there, ignoring speed. You'll slow down, but if you keep it in the power band, not all that much, and will likely end up passing semis and much larger trailers and RVs driven by people that don't know how or are afraid to use their engine. (You should see the stares from guys with big 3/4 ton pickups pulling trailers when they get passed by a Sienna pulling a trailer.)
To go downhill, crest the hill well below your target speed, and as you start to speed up from gravity downshift as much as your transmission will let you to use the engine's friction to slow you, and let gravity do it's thing. Keep your foot off the brakes. If the grade is too steep for engine-braking entirely, once you're about 5 mph over your target speed, brake hard to slow back down to well below your target speed (about 10 mph below) - repeat. (It helps to turn on boost on your trailer brake controller so that the trailer brakes a little ahead of the car when doing this.) Doing it this way gives your brakes time to cool between uses so that they don't overheat and will still be there when you need them.
Keep in mind that most cheap trailer tires are rated for a maximum speed of 65 mph, and being cheap chinese tires, don't have a lot of margin. 60 mph is a good target speed. Exceeding a tire's ratings for speed or weight can do cumulative damage that may not be apparent, but can lead to failure many miles down the road.
