Pete, I just went through the same problem but my trailer wasn't in such bad of shape. I took my old trailer to a shop in my home town and had it sandblasted and then they did a "metalize"process that sprays a zinc coating on it. You can paint over it but I like the gray color so I just left it plain. It will not rust from the outside now and rocks don't knock off the zinc. This is the third trailer that I have do this to and IMO the only way to go without going to new.
I also have shoulder problems and can't lift the bow up to unload so I put on a double roller system(check picture) and now I can unload the boat(on a flat surface) with one hand and it comes on easier than any trailer I have ever had. And it looks like it's new.
The boat sits on both rollers that are heavy plastic with metal pipe inserted with UHMW bearings that I made. I also installed new lights and gaskets. While installing the lights I found several bare wires and I wonder why my lights didn't short out before doing this repair job.
I do not know if the boat riding on the rollers will wear out the bottom "aluminum" but it's something that I had to do.
I had some extra bearings made if anybody is in need of a good setup.
Also if you were to buy a new trailer go with galvinized(sp)....
fop