powering a bi-pap (cpap) machine

we have a class c. i was wanting something that could charge during the day going down the road and be used only 1 night at a time. honestly, it would be used for the times we are travelling a couple days to our destination. i'd like to just be able to pull over and sleep at a walmart. our marine battery is a little hard to get to to run an inverter. i really don't want to have to try to figure out where to put a second marine battery.

I was thinking either the

5-in-1 Portable Power Pack Chicago Electric Power Systems or the
Duracell DRPP600 Powerpack 600 Jump Starter and Emergency Power Sourc