Insulating basement question

I'm in the process of fixing a previous remodel/addition that was put on my house, and have am curious how to go about insulating the basement ceiling/floor of the new addition. A sunroom was placed on my deck, with the floor joists for it extending into my basement. The floor of the sunroom is insulated only with fiberglass batts fit between the studs, with plywood sheathing underneath to hold them up. There does not appear to be any air/water barrier in place. The floor joists extend into my basement, so the insulation from the addition extends into the space of the rim joist cavity in my basement. Do I need to keep the floor of the addition open to rim joist cavity in my basement or can I seal the two rooms off and completely isolate the sunroom? I'd like to install XPS foam board into the rim joist space in my basement, but will providing an air/moisture barrier between these two spaces cause condensation problems? Thanks for the help, Adam