RVing is my life. Not kidding. In my 47 years, including the almost decade that I full-timed, I have lived nearly 1/3 of my life in an RV of some sort.
Your fears are valid. When selecting a travel trailer, never (ok, almost never) use the GVW of the trailer to match up with your tow rating.
I will say that the shorter lengths you're looking at are more forgiving.
A story. My friends had an LR Disco. Tow rating of 6k. They promptly went out and bought an ultralite 26' trailer with a GVW of 6k. Then they took it to Sequoia National Park. I drove it up with white knuckles, they drove it back. I should say they drove it part of the way back. Coming down the mountains the brakes overheated and they ended up with the trailer in a ditch against a tree. Once extracted, they continued driving it home where a good side wind started a sway, and all the equalizing/anti sway hitch stuff didn't matter. They ended up on their side and spent several days in a hospital.
There are two main reasons to avoid ultralites like the plague. (with apologies to anyone who owns one) 1 - they tend to be longer and see above. 2 - they are made with the absolute worst materials. Think cardboard and luan. I have been to RV shows where the display campers are completely wasted after a weekend; carpet matted, cabinet doors falling off or sagging, countertops that have settled because the floor is 1/4" OSB, fridges that are loose because opening the door pulled the screws out of the particle board frame... it's bad. Mom and Dad sort of inherited an ultralite from the neighbors that was only two years old. They have used it two seasons and it is absolutely wasted. In one 400 mile trip, they blew 3 tires because they used the cheapest tires in the smallest size that were barely capable of taking the weight. When the one tire blew, it sent so much shrapnel through the luan couch base that it ripped the vinyl couch like you shot it with a shotgun from underneath. The insurance company is covering it, but the repairs are scheduled to take 8 weeks.
Friends don't let friends to ultralites. You'll get 2 seasons out of them, tops. They're designed to attract people into RVing by saying "look how much trailer your RAV4 can tow." Those types of people are usually the kind of RVers who camp for 3 weekends a year; Memorial day, 4th of July, and Labor day for two seasons and then lose interest.
On the weight/length issue, I would rather see you push the tow capacity a little over the limit as opposed to adding more length.
If you were just recreationally camping once in a while I would say you can skimp a bit. So your water heater doesn't work, oh well, we'll improvise and call it an adventure. When your using it as a mobile hotel room for work, don't skimp.
Of all of the equalizing hitch/anti sway systems I've used, my favorite choice is a trunnion style equalizer with cam-style anti-sway. They're noisy, but they do both jobs with one apparatus and they do it well.
Trunnion style bars are less bulky and lighter, and they're also not as sensitive to overloading damage during installation.
If I were in your shoes, I wouldn't even be looking at new trailers. In the years between 1996-2001, the whole RV industry went kaboom. Every company got bought up by big conglomerates and things went seriously south. I currently own two RVs; a 31' 5th wheel from 1993, and a 32' Travel Trailer from 1992. Both of them, despite my consistent abuse are in beautiful shape while mom and dad's ultralite (from the same name/brand) from 4 years ago is a complete waste. Both of these examples are Keystone, but theirs was built 20 years after K-Z bought the Keystone name. On the downside, I do have to put up with Mauve in one and Mint Green floral print in another, but they are bulletproof rocks. I estimate that the 5th wheel likely has about 80,000 miles on it. It has been to Alaska, cross country 6 times, and across every southern Canadian province twice. Nothing has failed on it except the fridge, which (now that it's parked permanently at the lake) I replaced with a small residential 120v compressor fridge. The travel trailer is a Holiday Rambler. The walls have aluminum studs and the insulation is structural foam with an aluminum skin bonded to the outside and paneling skin bonded on the inside. The whole thing is a stressed-skin composite sandwich that can't rot even if you get a leak.
I'm rambling at this point.
Your tow rig and what you put behind it are also highly dependent on how far you plan to travel. If you're towing 20 miles to a state park, you can handle more white knuckles than if you're going 500 miles. Longer travel times can really harsh your mellow if you don't have enough tow rig for the size/weight. I towed the Holiday Rambler a lot with an F250 that was more than enough, but on longer days I was wishing for a dually. 8-10 hours of being "on duty" gets old.
They don't make em like they used to. Find yourself a nice older TT that hasn't been used much and enjoy.
