electrical problem in 5th wheel camper

Hi, I'm new and never done this before as I'm a bit off a computer novice. We have a 1992 Cobra Sandpiper. On our first trip this year, the water heater would try to light but not stay lit, then nothing. Next thing we knew, the under cupboard kitchen lights, range hood, and indicator lights for greyy water levels etc won't work. We were plugged into 30 amp service and hooked up to water. We are not mechanically inclined but we would like to know what the problem might be before taking for service if it is needed. We did flip breakers on and off. There are 3 double breakers and a bunch of little fuses. We think perhaps it has something to do with our battery but as I said we're mostly useless in this department.
Thank you so much in advance for any help you may offer.
Gammalouie