Not being that great at building things, I solved the medicine cabinet problem using two over-the-door wire shelves (got from CampingWorld). There's a tall and a short shelf on each one and they fit such that there is still room for items in the base of the cabinet, so I essentially have three shelves on each side.
What I'm trying to figure out now is the 'hole' under the counter. I have two wire baskets there now, but it's not particularly convenient getting thing in and out of them.
2014 FR3 30DS