I agree with Bikendan. Don't get anything bigger than 5000#. Even at that you won't like the pull. My first RV was a TT and my TV vehicle was rated to pull 8000# and the TT was rated at 7000# GVW and sold the TT after 1 season because didn't want that experience anymore.
Your best bet is to check with your state DMV to find out. I know that some states require a special license endorsement if you are driving or towing over 26,000 lbs. or if you are hauling paying customers.
Check with them.
Sounds to me like you may have a lemon on your hands. You also sound like you want to get rid of it, but need someone to justify your reasoning. My question to you is it worth the hassle and stress you are putting yourself through for 4 times a year usage? Sell it and move on to either another chapter in your life or buy a good used trailer. I wouldn't buy new for the little use you have.