HELP! Mushrooms growing in travel trailer

[ProwlerPowell]

Hi everyone, I Just bought a prowler travel trailer and when we went to look at what kind of work needs done there were mushrooms growing out of the wall. I am overly concerned about mold and mildew because of my allergies. Is this very dangerous and can this be fixed? I don't mean to sound nieve but I need to know what im looking at here? I bought the trailer to fix up for my family to travel in this summer. I looked all over the web and this site seems to have the most knowledgeable members. Thank You so much. I attached pictures as well.

[CamperMcGee]

I haven’t had mushrooms in my RV yet but definitely have mold and mildew if it sits for a while without use. I started spraying Dr. Burkenstock’s Mold Stuff in the RV generously when I’m closing it up for a while. It makes a huge difference and is also non-toxic which I like.