24” Adjustable wrench works to hold the ball, impact or wrench and cheater to tighten nut. Put the hitch in your vice if you need easier access.
I would never weld on the hitch or on the hardware.
I have 2 snap-on boxes, one is 35 years old and the other I bought in 2017 as my Retirement Box my 35 yr old box still works as advertised, You will never wear out a snap on box.
My thoughts are with you, cancer patient here, I have a small understanding of your plight, everyday can be a struggle. Hang in there and keep swinging
Snap On does not warranty abused tools, if a team has to buy a new torque wrench, $ 1400.00 is a drop in the ocean, they spend more than that on coffee for the team I am willing to bet