I'll second what Photomike said.
I have had water leaks in the past: I have had dirt in the pump diaphram. Take the pump head off the motor and clean the diaphram. You'll want to pull the pump to do that. Once you get the motor/pump assembly out, cleaning the pump is easy. You should have a filter screen on the intake side of your water pump to stop grit from lodging in the diaphram. Clean that screen periodically.
I also replaced the cheap little plastic isolation valves near the pump with brass ball valves (using shark bite fittings).
I accessed all my cabin plumbing by removing the stove and sink. Neither is hard to get out. Plumbing under the bathroom sink is another matter, that's impossible to get to. Some folks cut a hole in the fiberglass under the wash basin sink and install a round marine hatch (roates to open/lock) to gain access to the fittings.
Also, if you don't have one, (aftere fixing any leaks) adding a capacity tank to your water system will further reduce your water pump cycling.
BTW: I was skeptical about using Sharkbite fittings in the camper plumbing - but after 4 years and a bunch of rough miles, none of have leaked. They are certainly better than the plastic compression fittings that came with the camper.
