I have a 2008 Forest River Flagstaff 176ST MAC I'd like to install a cargo door so that i can access the storage under the booth seat from the outside of the camper. Are there any framing members that I need to be aware of? How are these things built, is it just a sandwich of aluminum, foam and press-board? Is there even any framing in the thing? I've searched the internet for pictures of them either being built or repaired, where i could see the structure, and i haven't come up with anything. Much thanks for any help!