In the world of RV trailers, try finding 40 year old survivors of the traditionally built stuff. Then look for the same thing with molded FG. You are going to find many, many examples. Heck, my Trillium
is 42 years old. And that is not unusual.
Sleep five? Thats a challenge. Typically family campers have one or more of the kids outside in a tent. And realize to get more beds you get less of everything else. No places to sit (unless you take up the beds every morning), no bathroom, etc. Sometimes people pull the trailer with a large van, then put sleeping quarters in the van for kids.
A 17 foot Casita
Spirit standard (no bath) with front bunks and side dinette would sleep five as well.
RVs are not made expedition ready, except for some rare, and VERY expensive versions. Whether its a FG trailer or something else, they are not built for jeep trails.
Saw one of these in Alaska, you can take it anywhere. Cost? Its way over my budget.
Where have you "heard" Scamp
has durability issues? I'd like to see the source.
Ground clearance and relatively wimpy frames hold back most FG trailers. Scamp is built with rivets, so those might be challenged by rough terrain too.
There are a variety of threads out there with people using their Scamps and others on FS roads. Some look to be lifted.