I have used 5200 many times on boats and can tell you that it will not easily come off. It is not particularly sticky before it is cured, rather more like any other caulking so you will need to figure out some way of tacking the two components together until it cures.
They also make 4200 which is what I suggest you use for anything you might want to remove in the future. 5200 will rip fiberglass apart before it can be removed so only use where you never want it to come apart. It also cures under water if that is ever needed, like in a tank just to get you home.