Water infiltration can be the kiss of death for a TT. If you want to maximize it's life, you need to keep on top of caulking the roof and other places as it's needed. Regular inspection is important. An RV cover helps in the off-season, especially in wetter locations. If you use a TT a lot in the winter, moisture from the inside (from lack of ventilating it out) can cause problems and even damage. Don't leave tree droppings on the roof and awning.
I would say frames are another weak point. Some frames flex a lot and can eventually develop cracks and failed welds. If you do a lot of long distance travelling with a weaker type frame, it won't last as long.
Fiberglass is great but it can delaminate. I'm not sure of all the exact reasons but I think it can be due to poor construction at the factory and I think also from moisture build-up in the walls from continual high moisture levels on the inside (moisture migrating to exterior wall surface).
Keeping up on repairs and maintenance is really important. Exterior moving parts should be regularly lubed (with correct stuff) and use slideout seal treatment. Waxing the exterior with a good wax helps. If something fails, replace it with the same or similar product and do it correctly. Some components are destined to wear out or fail regardless of what you do but you can do things to extend their life.
I think a slide topper is a good idea and we plan to get one.
Simple preventative action can help. I read recently where someone had a toilet valve fail while they were out shopping. It flooded the floor and did extensive damage. IIRC, the entire unit was a write-off. Maybe it's a good idea to replace the valve every few years? I think we will shut the water off now when we go out somewhere for a while.
Otherwise, stay away from RV shows. ;) One day you may see something you just have to have, even if you don't really need it.