Although the best solhtion for the CPAP solution is the installation of a 12v outlet dedicated to the machine, never forget that the proper outlet installation is a major modification to your coach, and should not be attempter by the technically incompetent. Rather, have an electrical engineer experienced with delicate medical equipment to plan and design the structural design, and anexperienced RV technigian to perform the actual installation tasks. Then have an electrical inspector approve the entire job.
It took me about 30 minutes for the entire job.