We have several 12V receptacles near the mid-point of our motorhome, but the bed is in the rear with no 12V receptacles back there. We just plug a small 300W pure sine wave inverter into one of these 12V receptables, plug a light duty household extension cord into the inverter, and then string this cord back to the bed each evening to power the DW's non-humidifier CPAP machine. It works like a champ and her CPAP machine only uses slightly more current than it would if using one of those expensive $$$ bricks made for it that merely allow you to plug it directly into a 12V receptacle.
Why spend the effort and some money to put a 12V receptacle back by the bed AND THEN spend some more money for a brick so that we can then use the 12V receptacle for the CPAP machine? We already own the inverter for other reasons, so why not use it for the CPAP machine at night.