Mold/Water in the spare tire?

So on my ford fiesta that I had for like 6 years, it was a rebuilt title when I brought it. Nothing really happened until I got rear-ended like 2 years ago, was fix and I did not worry about it so much. Fast forward to now, I'm like why am I getting so sick, driving for 2 years to only find out the water leaks, have turn into mold + yellow water. Like we have mold icicles on the spare tire plywood, like 5 inches long. All sorta of red, green, and blue dots. Water that wicked up as high as the roof line for the hatchback. It was like at least 5 gallons of water inside the spare tire area.

I traded that in for a nissan sentra. Yeah, the yucky Cvt...but clean, no accident, non salvaged/branded title.
I think that is the smartest move for "health wise." I never had the problem like that with water.

What is your opinions?