Inside of TT covered in mildew

We have a 2011 Jayco Jayfeather EXP 26P. Had a planned camping trip this weekend and the state park we were staying we about 30min from where we had the TT stored so we packed up truck and headed to get the TT and hookup and straight to the campsite. By the time we got there it was dinner time so we parked camper and head to town for dinner and supplies. It was 9pm when we got back and prior to that I did not really spend any time in camper other than to walk in and out to get something really quick. Anyway we get back and walk inside and me and he DW notice mildew EVERYWHERE. It is on the cabinets parts of the wall and on the bunk mattress and dinette seats, couch, a wooden bowl on the table, hats, everything... We just stared in disbelief. Luckily we were only camping an hour + from home and decided it was not worth staying in the camper and possibly getting sick so we packed up and went home. We will start the cleaning process today and will most likely toss a lot of things but wanted to see if anyone has run into this before and any suggestions in cleaning and sanitizing the TT and what could have caused this to try and prevent it in the future. The TT is only 2 -3 years old and we got it new and have never seen anything like this with our last TT or this one. We are in the Atlanta area and has been a wet spring/summer and the only thing I can think is that upon storing it after last use 2 months ago I left the bathroom vent open and maybe the moist air got in through there and couldn’t escape. It is stored under a pole barn and there are no leaks. If the bathroom vent was the problem I don’t get how the bathroom as little to no mildew in there but the rest of the TT is covered.