I have a Montana 5th wheel (3465sa) the w/d are in the bedroom so it's a one unit deal.
I checked out their web site and I see a few units with the washer option in the closet by the front door - I don't know if that means it could be a stackable unit or it it would be a combo unit.
http://www.keystone-montana.com/index.p ... ans&coast=You could email Montana or just call a local dealer, they'd be able to help you.
Good luck with your search - I do love my Montana and I think they're awesome !!!