I don't know of any site that will give you detailed drawings of the different configurations for subfloors in Keystone products. You can look through the old brochures on the Keystone website. In some of them, they list the various ways that they build the RV's. Some show cut-away drawings of the structure. That will give you some idea of how they are built. Otherwise, it's "rip into it and find out the hard way"
Keep in mind that it's not a simple one or two day job in most cases. You're dealing with a sliding patio door (from what you described) and probably a 4-6 foot area that will need to be replaced. Between carpet, vinyl, walls and bracing, it could get to be very demanding. Unless you have at least average to better than average carpentry skills, I wouldn't try it.