Recently, I noticed that I was sneezing when I used the toilet in my rig. I finally figured it out this morning. There is a ledge where the plastic shower walls sit on the shower pan. When I looked closely, I saw the dreaded four letter word MOLD.
So I got some Clorox and a cheap toothbrush and went at it.
I carry a small spray bottle of bleach with me and spray down the whole shower every week or so. In that closed space, especially in the heat, it is a greenhouse for mold.