Welcome to the forum!
There are a number of us Argosy owners here.
The floor is the main weakness. It can suffer from dry rot if a leak has not been fixed in a timely manner.
The rest of the construction of the shell is aluminum, the frame is all steel. It is built on a P30 RV chassis. Depending on the year you may have a rear airbag suspension and drum or disk rear brakes.
The interior is NOT stick and staple. The interior skin is normally aluminum covered with a vinyl sheet. The interior furnishings are attached to the interior shell with screws and rivets. Most of the interiors are made with a combination of thin plywood, extruded aluminum and sheet molded ABS plastic. This is the same as the interiors of the same vintage Airstream trailers.
10 MPG Downhill with a tailwind, maybe
Approx weight will be in the 10K range max on a 24. My 28 is maxed at 12.5K and I never have it that heavy.
The only items are a hard to get right now are the window tracks and sometimes the window seals. The rest of it is still available for the most part.
The only areas I have seen a galvanic reaction is where the end caps meet the main body. This is an area that then experiences surface rust. I have not seen any on the underside.