For 120 volt electric, I use a no-contact voltage tester. For 12 volt
, I use a small 12 volt battery charger, a 12 volt jumper light, a small multi-meter and for towing lights, a 7-way tester.
Water is easy on my trailer and is all visible above the floor except for about 4' crossover.
My trailer didn't come with any warning systems. I installed a new CO detector, a new LP gas detector, and a new smoke detector. My fixtures, (like furnace, water heater, and air-conditioner,) plus appliances, (namely, refrigerator and cooking stove/oven) were all OEM installed in 1976. I replaced them all.
Old, second hand, gas appliances and fixtures doesn't work for me. The good part about replacing everything . . . is everything works like new. :-)
Oh, take the screen off the kitchen faucet water spout and clean it. It's probably clogged.