Pimples or bumps behind wallpaper

I have also found them inside my travel trailer on a wall that doesn't even have a window. There's not a lot of them and absolutely no indication of water damage anywhere. As noted, they are hard, sharp little bumps, not bubbles.

I have seen these same bumps in mine I think they are caused the solvents used to bond the wall paper to the inside wood as they flash off. Sometimes you can smell these solvents in a brand new MH.

I have a similar situation under the back window in my Leprechaun. I haven't done anything about it but I guess I should, in case it is mold. The bumps are hard and rather pointy so I was think crystals.

Really puzzled on how water is to blame.

I had the same problem in the same place.
A water hose left spraying on the window showed that mine actually came from above the window. Water follows paths that can fool anyone. But my exterior was aluminum which I believe has more places for water to leak.

Although the bumps are showing only in that spot, you may find more below the present line when you remove that panel.

If you can find the correct panel, I would cut it a little high and maybe raise the border just enough to cover but not high enough to be noticeable from the rest of the room.

You can get matching interior paneling at All-Rite.

We just experienced the exact same problem, only ours was located to the right of the door when you walk into the camper. Ours started just below the knee and went to the floor. I decided since the wallboard/wallpaper was bubbling that it was ruined and would need to be replaced anyhow in order to make it look presentable again. So, I took my knife and cut open a spot to see what I was dealing with and it was mold....lots of mold. I ended up cutting out that section of paneling and revealed a pretty good amount of moisture in and around the frame of the trailer. I'm still not sure where the moisture came in from (I dried it out well with fans and such and it has rained a few times since...no leaks or moisture has reappeared). I read somewhere on this forum that condensation around the doors and windows, especially in humid places here in the south, can and will form (sweating is what they referred it as).

On a side note, my paneling and trim looks almost like yours (my TT is a jayco). Does anyone know of a place to order replacement boards or even how to identify the correct panel board number to order?

Is there a chance that is was caused from condensation on the window running down and making the wallpaper damp enough to cause this?

Rather than water, I'd rather think the chemicals in the wall construction (traces of chemical moisture, not necessarily water), heated up and came to a boiling point. Remember, different chemicals have different boiling points, some much lower than 212 the temperature for water.

It's possible there was a chemical reaction, which resulted in a "boiling", thus the bubbles, and like someone else said, it then crystallized. I'm just guessing here. Not every blemish in an RV is the result of "water damage."

Following :-)