No inverter on a 23B. Only things that will work is the 12v system, aka lights, water heater & frig (propane mode), furnace, radio, etc. No microwave, ac, no traditional wall outlets.
The cpap should not be a huge issue. I purchased a 12v power cord for my cpap. I also installed a few 12V outlets near the bed. Your new 23B might have outlets nearby.
I do not have the OEM mattress pad heaters. I do use aftermarket ones. Typically in cool weather we find a campsite with electric. If we do not, I place a few fleece blankets on top of the mattress before making the bed. Bring a long a few extra blankets.
I have a small inverter that I can plug into a 12V outlet that can run my electric mattress pad, but have never done it. If I recall my mattress pads pull about 180 watts each when on high.
If you have enough batteries and solar, it should not be to big of an issue using a small 12V plug in inverter. Just note, there is a lot of inefficiencies using an inverter, so your batteries will deplate a bit faster.
As for voiding the warranty, the can only void something you changed. For example, if you added an outlet off of the microwave outlet, and connected the wired say backwards, and say the microwave fried. They would not cover it. That change would not void the bathroom outlet warranty.
Have fun with your new HTT