solar power for dry camping & cpap machine

I'm not suggesting "whole house" isn't a solution for some but there is more to it than just plugging the trailer's main service cable into the inverter.

absolutely correct

3kw and RV shore cord is not needed for CPAP and way to much for (2) batteries
run stuff like you have shore power ?
means have many KWhr of stored battery power
and then its still limited, MW for minutes only, coffee maker for a pot OK, water heater, fridge etc.. on propane, NOT electric, No A/C
there is many times the energy of (2) GC batteries stored in (1) gallon of gasoline
(1) gallon regular Gasoline = 33.44 KWhrs of electricity
approx 2786 Amphrs at 12v
(2) GC will apprx 240 amphrs if run dead flat, 120 amphrs to 50%
i gal of gas has over 10 times the amount of energy as two fully charged GC can hold

a generator is indispensable , Solar is adjunct for most of us, along with a large battery bank

can you run a CPAP with inverter and batteries YES
can you run the whole RV like it was on shore power with only two batteries NO.

if you accidentally leave something on, or try to run a high power appliance with a small inverter it will alarm and shut down
no harm done to the batteries

BUT use a 3kw whole RV with (2) batteries
and you will run a very real possibly of killing your batteries
the fridge will auto shift to AC, or the water heater, or you will forget to unplug the converter , try to run an electric heater ? etc..