We done a few things to ours to update it. Our 5th wheel is 20 years old and we really like the floor plan but needed a desk and wanted an electric fireplace like some of the newer models.
We added a desk in the dining area. like this http://amazingmagictable.com/2tabledesk2.htm
I bought a fireplace insert online and removed a three drawers from a cabinet under the counter where the main TV sits. With a little modification the fireplace insert fit perfectly.
We added small storage cabinets between the windows in our living room slideout.
The bottom step up to the bathroom area was converted to a storage compartment by adding a hinge on the tread so it would lift up.
We replaced the FlexSteel recliners with two from Lazy Boy for more comfort.
In the bedroom there was a counter where the bed partially slid into when the slideout is in the travel position. There was still enough room to add four 3 drawer plastic storage units from Walmart.
Yes modifications can be done but you have to be concerned about weight balance, structure elements, plumbing, electrical and other stuff the manufacturer places during the build when tearing out existing cabinets/walls.
