Your water spot is a puzzle and I have a personal comment to make. On our maiden voyage with our new 13' Scamp
we noticed water "spots" on top of our bed. (We do not have an air conditioner) We also noticed a lot of moisture condensed on the inner fiberglass walls. We soon discovered that since we were keeping our trailer tightly sealed (all windows
and door closed) when the outside air temperature changed from warm to cool, the interior "sweated". A couple things we now do to reduce the "sweat". #1 we keep one window and the ceiling fan vent open a crack thus providing ventilation and air movement (no need to turn on the fan). This seems to prevent the drips #2 We cover the "escape hatch" which is just above our bed with a simple cover that catches drips (and seals out the morning sun).
I do not have a photo of my "drip catcher". The photo I did post shows a similar "system" that I use as "black out shades" on my windows
. It is modified to use on the ceiling. Basically, cut one rectangle of "Roc-Lon" (drapery black out fabric available at most fabric stores or online) to a slightly wider width than the ceiling opening and about 6" longer than the length of the opening. Fold over the short ends about 1 1/2" and sew 1/2 inch from cut edge to form two channels to run a rod* through. Note: there is no need to "finish" any of the cut edges as this fabric does not fray. Cut a rod 2" longer than the width of the channel and place rods through the channels. Attach the rods to the ceiling with 4 "cubicle clips" if you have "rat fur" on the walls/ceiling. Staples® Cubicle Clips, White, 20/Pack | Staples®
We have found that the cloth absorbs the water and dries out easily.
*For rods I used camp tent poles cut to size (you can use old ones or get a replacement set from sporting good shops) You could use wood dowels or any number of things. (Don't use something that rusts) Actually, you don't even need the rods for this to work. I like the rods because it keeps the cloth closer to the ceiling thereby blocking out more sunlight. You can use Velcro (as seen in my photo) to attach to "rat fur". I prefer NOT to use Velcro as with multiple uses, on and off, the "rat fur" gets long, pulled threads and the Velcro does not work as well because it gets matted with "rat fur" fibers. If your ceiling opening has a wood frame you can screw clips onto the frame to hold the cover.
Hope my comments help you find your water source and solution.