Hey there, congrats on the new Gateway and enjoy the forum, a lot of good folks with plenty of knowledge they are willing to share.
I would check when manufacture date was on your rig, my 2014 was built in 2013, same year we bought it, anyway, my wife and i dry camped in Montana last summer for 10 days, we had no problem with batteries staying charged at all. I would suggest doing a load test on each battery and see if they pass. Our unit does not have a residential refer but with LED lights and stereo being used while we were not hooked up to any power, i still had enough juice left to raise the front jacks to hook up to the truck.
As a mechanic for 30 plus years i have seen new batteries fail so may be worth checking out. We do not have a shut off switch on our unit either so while at home are hooked up to an extension cord for the most part. Also after 3 plus weeks at the dealership getting some work done there was still enough power to hook up to the truck and i doubt they had the unit hooked up to any power while there.......