Darrel, feel free to ask away, I'm only too happy to help if I can.
I first bought a plastic bin as a catch tray. They come in many sizes and may work for you. However, for me, I decided upon building a bin of plywood to my exact size and fiberglassing the whole thing. Under the new bed we built, I left a door to give access to the storage space under there. I made the catch tray so that it would slide in that opening. As luck would have it, when I pull the tray out it ends up directly under my hanging frame to which we hang the shower curtains.
Yes, we leave the pot on the stove. I first heat the one pot and regulate the temp with cold water and turn off the gas under that pot. Then the wife starts her shower and I turn the heat on under the second pot. As she gets down in water I add with a ladle if needed. She does the same for me of course.
A lone person could do all of this due to the small size of the trailer. You simply reach out through the joint in the curtains and the pot is within arms reach.
As for splashing, we never get a drop anywhere outside the enclosure. Remember, that shower head only works when you depress the button. So if you reach outside for some reason you merely turn off the flow before doing so. We lay out our fresh clothes on the dinette before showering then we step out onto the carpet, get dressed, pump the water back into the jug, and we have the whole trailer again. No bathroom space lost!
We wipe the curtains dry, fold them and put everything, pot, pump, thermometer, and curtains into the tray and push it under the bed and we're ready for another day enjoying our trailer.
Here is a picture of the catch tray I built.