This is what I would do.
1. Find the payload number on the drivers door of your truck. (xxxx)
2. Added together your weight, your wife, kids, dog, etc. Subtract that from the payload number xxxx. = (yyyy)
3. Determine the weight of stuff you may carry in the truck (hitch, firewood, tools, bikes, etc.). Subtract that from yyyy. = (tttt)
4. Take the weight of the trailer as it weighs on the lot at the dealer (aaaa), add about 1250 lbs to it. = (bbbb) (loaded trailer weight)
5. Multiply bbbb x 15%. = (cccc)
6. Subtract cccc from tttt = (jjjj)
7. If jjjj is a positive number you have some cushion. If jjjj is a negative number pick a lighter trailer.
The 1250 lbs is an estimation of how much stuff you are going to carry in the trailer. The smaller the trailer, the smaller this number will probably be. The more water you carry in the tank plus, camping charis, grills, etc. that you carry, the higher this number will be. No kids, less stuff, etc. 1250 lbs is probably a tad on the high side considering a 7400 lbs trailer. Also 15% is a little on the high side. So there may be a little fluff in the calculations but this is just a SWAG to get you close.
