I have a 27DBK too. Make sure the switch in the trailer for gas is off. Open the cover for the water heater and there is a big on and off switch, just turn in on. If you want to run by gas turn the switch to off and then you can use the inside gas switch.
I leave it on electric as long as my water heater is full of water. If the trailer is not hooked to electric it does not go on. Just make sure you turn it off before you empty the water heater, you will burn the elements if you don't.
Renee and Wayne
2018 Salem 27DBK,
2004 Dodge Ram 1500
2 kids, 2 Grandsons, 1 Granddaughter, 3 fur babies