have you weighed your trailer to see how much weight in on your trailer axles? That would be a good starting point to determine if G rated tires are a good option. If you only have 2000 lbs on each tire, going to G rated tire will be way overkill and will be pretty rough on your 5er and everything inside going down the road. I did upgrade our rims to 16" and the tires to XPS ribs and have gone 10 years on them with no issues, (yes i know i am on borrowed time and will be replacing them before camping starts this spring).