Keep in mind that even on a catamaran, things can move. Cats don't like weight, so if you have bookshelves, for instance, consider shelves made of doweling (painted, patterned, whatever) over solid wood planking. You could have hooks and
line instead of bungees to keep them stable. Things like glass stowage, coffee mugs, plates and cutlery have to be thought through. I would suggest that for a cat, a good place to get ideas would be in RV "lifestyle" magazines, because the range of motion and stowage solutions are similar in both "vehicles". I've seen some very clever things in RVs that are easily adaptable to boats, mono or multi.