Regarding traits: you can have Rc<Trait> (by casting from Rc<your concrete type>), but not RefCell<Trait>. The reason is that Rc is a pointer, so the size of Rc<Trait> can be constant regardless of the size of the type implementing the trait. But if you actually want a weak reference inside a refcell (as opposed to the other way around), RefCell<Weak<Trait>> should work fine. Also consider the Cell type, which has a more limited API than RefCell but zero overhead.
Regarding everything being destructed at once: that’s called an arena, and there are crates for it: