There are a number of ways to skin this cat:
You can buy a Duracell "power pack" (DRPP600 is the model) which is essentially a 600 watt inverter coupled to a small battery, which is intended to be used for radios when off the beaten path. I've read about people using that with good luck with their CPAPs.
You could get a battery from the CPAP maker and a charger. These will not be cheap, but a battery a night for each CPAP is doable. This is the solution that likely takes up the least amount of space and weight.
Of course, a 1000 watt generator will do the job, but even the quiet Hondas may be a bit of a racket, and there might be times of the day where running a generator may be forbidden.