One trick I read here somewhere that I use in my motorhome (which would be slightly less convenient for a travel trailer, but still isn't a bad idea) is to write all the various departure checklist items on clothespins and clip them all on the sun visor above the driver's seat. When an item is done, the corresponding clothes pin gets pulled off and stuck in a bag or whatever.
I have maybe a dozen or so clothes pins so far. From memory, they include TV Antenna (cranked down), Electric (unplugged and cord stowed), Tire Pressure, Awning, Entry Step, Bedroom Windows (jalousie windows shut as per instructions), Rear Window Blind (open, so I can use the rearview mirror), Outside Compartments, Count Noses, etc.
It's very easy to forget something without a checklist of some sort. Paper or smart phone apps or what have you also work fine.