Can you get a picture of what you're talking about "spools"? I just looked under our
Uhaul by the door, and I've been under ours many times previously, and can't imagine what you're describing as spools. The floor sets on the trailer frame with large flat soft washers between. There is a lot of support in the door area, with two frame brackets for the body bolts in the door area, and one just ahead. It is very common that the body bolts, those large flat head bolts known as elevator bolts, that go through the floor and held by a nut underneath, to rust away in the floor. Some can rust so much that they
fall off underneath, others will rust down to almost nothing where they pass through the floor and will break off if you try to turn the nut with a wrench. First thing you should do is check for rot in the floor wood. It seems common for water to leak in around the door, plus in many other areas of these trailers where it can't be seen. Since the floor covering is out this is the perfect time to replace all the body mount bolts. Some are also located in the storage areas and under the counter area. If you do have rot in the floor you may have to replace a section. I had a very small area at the floor edge in the doorway. I repaired it with
fiberglass resin and cloth. It was only on the edge. I think you'll find other areas of leakage if you do a thorough investigation in a heavy rain storm. Typical areas are around the
windows, especially the side
windows, marker
lights,
tail lights, door seal, door hinges, and possibly the roof seam. A blowing rain can be driven in the stove vent. These trailers have a good frame, but I have seen pictures of rust through in them. Check it out.