Since you're considering more storage... (lucky dog!)... You might want to consider changing your doors to two 3'-0" or 2'-6" solid core slab doors, and give yourself plenty of access to your storage.
You can cut an opening in the door(s) for window(s) and come out pretty good on cost. Just add a sheet of plywood and/or gypsum to the inside and beef up the mass. If you go that way, lemme know, and I can post up part of the prints from the studio build to show you how to do the stops/gaskets to make em' as airtight as you can.