Hi Bob; and welcome to the Sunline Owners Club. I hope you can soon get your camper into shape and start enjoying it.
Click on the "Files" link at the top of any page and follow the links along to download a pdf of Sunline's 1997 brochure.
Sunline used Weyerhaeuser Structurewood. Technically this is not particle board--it is OSB or oriented strand board--the wood flake stuff seen on most new home construction. See Wikipedia for some of its properties.
A big advantage of OSB is that Sunline got it in big sheets for 1 pc. floors. A big disadvantage is that it is not meant for outdoor use and certainly not for puddles of water to be left standing and soaking into it. The Sunline underbelly is covered with a Darco membrane and that should be inspected at least once a year to ensure it is intact. So the only damage the OSB is susceptible to is internal leaks either from water getting into the camper or leaking plumbing.
Discolored vinyl flooring is the first hint of water damage to the OSB. Look for very obvious irregular grayish blotches. If you have those the OSB is likely soft and you'll be able to feel spongyness pushing down with your thumb. That is not good and would require some rebuilding which some of our members have done.
It is possible to restore soft OSB with an epoxy product designed for that. I have no experience with it and don't know anyone who has used it, but there may be some members who can add their .02 on that subject as well. Type "epoxy rotten wood"--without the quotes--into Google and you'll get all kinds of hits with information.