"The camping season is almost over here in canada but will look into some new tires in the new year. I was wondering if just adding 5 pounds of air in my rear tires would do for now. I'm only running 35 pounds as marked in my truck door. Tires are rated for more."
I would air those tires up to the max sidewall cold pressure. This will likely help your wiggle significantly. If it doesn't completely eliminate it, you aren't out anything. I would try that first. We had to take our trailer in for warranty work a few months back. I didn't air the tv tires up to tbeir max. It made for a miserable tow. I have p tires on my truck, but will likely go LT when replacement time comes.