I don't know how common this issue is, but this is the problem and the solution:
Problem: My shower drains into a shallow pan that sits in a very shallow part of the bilge. There is no room to put the standard off the shelf sump system (plastic box with a bilge pump and float switch inside). The factory solution was to install a diaphragm pump remotely mounted with the hose connected to a fitting at the bottom of the pan. The pump is operated by a momentary switch in the head compartment. The issue arises when you are taking a shower, the shower pan quickly fills with water and you are standing in ankle deep water by the time you are done. The momentary switch to activate the pump is out of reach while standing in the shower. I considered just replacing the momentary switch with an on/off switch but I did not want to risk either forgetting to turn it off, or having to remember to turn it on before getting in the shower.
I put a tee fitting in the shower hose line and installed a 12v pressure switch in the tee. I then wired it back to the momentary switch. Now, whenever you turn on the shower, the pump automatically turns on, shut off the water the pump turns off. Now the pump keeps up with the shower and no more standing water in the head. After a shower, any residual water that makes into the drain pan can be easily removed with a brief press of the momentary switch.
Very cheap and effective solution. A few bucks for plumbing fittings and $22.00 for the pressure switch.
I added the 1/2" Tee where the shower hose connects. A 1/2" nipple at the bottom to connect the shower hose, and a 1/8" bushing facing the wall to accept the threaded end of the pressure switch which is installed from behind the wall through a small hole.
The pressure switch an tee fitting. I decided to use brass instead for the aesthetics, but nylon or PVC will work just as well, and for less money.
This is the box for the pressure switch. $20-$25.00 online or available at most auto parts stores.