If you left the battery hooked up then you likely drained it. If you have a trickle charger, charge it tonight. If not you can charge it off the tow vehicle if it can be revived (usually can). Disconnecting the battery prevents parasitic draining from things like the stereo faceplate, microwave clock etc. Investing in a battery disconnect switch makes this easier but you can always just disconnect 1 terminal on the battery. If you disconnect it entirely, pay attention to which cable goes where as they are not the same as on a car. Also turn your propane off between uses too. Hope this helps you.
2014 Crew Cab Chevy Silverado 3500 4wd Duramax/Allison
2014 Sabre 34REQS-6