roof with Styrofoam and no rafters

[dandaman]

I just bought a 2006 Starcraft Travel Star xlt 28 foot travel trailer ,I knew had roof damage, when I get it home I see that is coming in from the master bedroom skylight it is a really bad. It wasn't able to be fixed so I pulled back the rubber and the Luan just fell to pieces and as I tried to pull the styrofoam up it was breaking in my hand. So now I have all the styrofoam off and there's just a big hole over the master bedroom. It's like a six foot span with no rafters. I planned on taking the whole roof off because there's a little water damage in the back and replacing the membrane but I don't think the foam is going to survive that has anyone ever added trusses to this kind of trailer and just put plywood on top i was planning on taking all the foam out. I am very lost on this rebuild I am a carpenter but I cannot put plywood down without trusses. I want to redo the whole roof I've already ordered the membrane, it will be here this week I was planning to have everything fixed by the time it got here but I am lost, trusses in the back area will not be too big a deal because there are walls keeping the roof flat, should I just fix the bedroom area and pray all the foam is good enough to hold plywood on top I was going to use wood trusses that will be held on by some pieces of angel iron but that is such a long span 8 feet for a sheet of plywood I'm afraid that wood might sag. I have never seen any type of construction like this with just foam boards and no Raptors the builders had to know that this will not last long very bad design. Is there anyone here who has ever rebuilt a trailer like this I'd love to see some pictures ideas of how I can hold my plywood up in that kind of stand I know I would need them on four foot centers I would probably due 2 foot. Would that make my travel trailer too heavy it's already pushing the limits of my07 Dodge Ram 1500 5.7 Hemi I don't know if I can pull anything more than what the trailer already weighs any help would be appreciated from anyone I am new to this form and I can't find nothing on the internet about this trailer Jayco bought them after 2006 so they can't even give me parts for it I'm not afraid to fabricate I would just like an idea what to fabricate to inch and a half tubing is not a lot to work with thank you