Every potentially available cubic inch of storage space is like gold. Look around and see what might be available. You can also make existing spaces more efficient like installing drawers in cubby holes beside the bed. You might under-utilized space in dinette seating. 'Course, this will require some carpentry skills and tools.
Often the waste and water piping under sinks is installed at the factory in a way that prevents good use of the space and you can re-route the piping out of the way.
TTs often have blank panels in cabinetry with no access. You can simply pop the panels off as they are just stapled in place, then install a new door(s). A door could be from another model of your TT so the finish matches, or you could get custom ones made to fit the openings or you might be able to buy something off the shelf at a big box store.
In our current TT there was a big empty space between the shower and bedroom wall. I cut the wall open and created new cabinets using doors from other models of our TT (first 2 pics). Pic 3 shows a custom door I had made up at a shop to go where there was originally a blank panel. Pic 4 is drawers I built for the original cubby hole beside the bed. Pic 5 is a pair of drawers I made up for behind a dinette seat and I raised the existing surface about 6".
It seems to me after going to a number of RV shows that TT manufacturers don't put much thought into efficient use of cabinets and storage spaces and it's more about the lovely wood finishes. I think there are a couple of brands/models that do a better job.
Some ideas:




