Alex,
I'm going to go out on a limb here and suggest that you DON'T use this trailer as the basis of an expedition/camping trailer! Before you think I'm just a spoil sport, listen to my reasoning (and the fact that I built a camping trailer starting with an old boat trailer).
If you look carefully at the trailer and evaluate what parts you are going to want to keep, you will find that there really isn't much. The sides are peeled back and will need to be replaced. No doubt the wiring is shot. You'll need to replace the tires no matter what. That old coupler will need to be cut off and replaced. You may want to replace the springs, and depending on how hard you want to "wheel" it, the axle may need to be replaced. You mentioned that the bearings spin freely, but you still may want to replace the bearings. I found with my trailer that the old bearings and grease seals are very difficult to find. What you are left with as a bit of rusty metal in the shape of a trailer frame (that may not even be the right size for what you want to build).
Here's my point. If you have the skills to build your own trailer you would be much further ahead to start with a clean sheet of paper and design the trailer just the way you want it. You will spend much less time trying to rebuild the parts you don't like and replacing all the parts that are too old or worn out to be serviceable.
You will be much better off starting out with a drawing of what you want, a pile of parts, and a few lengths of steel.
That said, the trailer would make a good utility trailer for hauling junk to the dump.
Joanne