Your red light should come on momentarily while WH tries to light. Once it does, the light should go off. If it doesn't go off, then that means that the WH did NOT light. It will try this 3 times then "lock out" & not try again and the light will stay ON until you turn the propane side off.
If you're using both propane & electric to heat the water then it should heat up faster. Just because the propane side is not firing up during use may just mean the the electric side is doing a good job or the water temp. hasn't dropped enough for the heater to fire up.
Also, the electric side can be used alone not just as a "backup". If you're at a campground & hooked up to the proper power requirements for your RV (30 or 50 amp), why not use their electric to run the WH and save your propane?