RV cabinets are generally made and installed as a completed unit. In this case, I would think that the top was fastened when the cabinet was in the cabinet shop. The top was likely fastened from the underside. If it has a door or drawer on the front, look in to see you can see any screws going into the top. If so, remove them and hope the top comes off. Not likely it is glued on. I think you may have a hard time accomplishing your task. Probably very tight space. There is the possibly that you might get it off, but may not be able to get it back on. Good luck.