Most anything can be done if you have the time and the inclination to do it. I added 6" to the bed in our 16ft Casita
. Just make sure that if you modify or take the cabinet or closets out, you put something back in place that provides some kind structural integrity. The fiberglass cabinets are critical to the support of the roof and maintaining the overall shape of the fiberglass body. Without support, over time the body will turn into something akin to a squashed jelly bean.