After 1800 miles on the trailer after installing it I thought I would let you know what I found out using the holder.
I was impressed with the suction cup, the holder never came unmounted, 300 miles was over fairly rough roads and I had expected it to come off the wall. The suction cup has a screw device to ensure you really get a good seal to the wall.
The holder will only hold a standard size roll of TP. (Not a Jumbo) The indentions on the inside where the spring rod goes are shallow but it did hold the roll in place.
The holder is a top feeder and dispenses the paper with little pressure and if a little end of paper is sticking out the holder there is no need to lift the lid to dispense the paper.
I did not shower in the trailer but I did spray shower water around and over the holder, the paper on the roll stayed dry, only the little piece of paper hanging out the dispenser got wet.
Now for the cell phone holder, water collects in the holder on top as it would in a soap dish. When the top is lifted the water runs off the back and did not appear to get the roll of paper wet.
I would give it a 7 out of 10. Stays stuck to the wall, feeds paper easily and keeps the paper dry. Loading the roll and getting the spring rod into the indentions can be a bit of a challenge. Not a heavy duty product but it got the job done.