YES... I saw no beams
plywood with fiberglass outer laminates
walls hold up the roof looked like there is NO studs/framework inside the walls, there may be some stiffeners at each corner where the walls meet.
if 50% feels soft and spongy ... expect at least 75% needs repair.
The repair is not going to be easy...
google fiberglass boat core repair to get an idea what's involved.
It would be uneconomical to attempt it.
get the trailer out of the weather for months to dry it out
repair can be either of two methods .... Inject OR Replace core
but the fiberglass looks very thin........ so that makes both process much harder.
Such a big area ... the amount of resin will be very expensive... Use polyester.
Epoxy will kill the bank of England.
you might extend the life just a bit by using a product such as inject a deck