Try Chlorox Cleanup Spray.
Try it in an area you can't see like under the seats.
Chlorine is used commercially for mold remediation, so it is a good use. The natural woods shouln't bleach, but test it anyway.

one part bleach one part water.....rinse apply as needed

A pressure washer with a bleach solution will take care of that no problem. They are easily rented from a hardware store, and you may find all sorts of other things to clean too.

lemon oil and bleach

Bleach mixed with dishwashing liquid..Scrub lightly, allow to set for about 5-10 mins, then rinse. After ding that, allow to dry thourghly and seal with something like KILZ or a simuliar product. Then paint whatever color you want to! Be Blessed and Good Luck! Rev.Susan

It's hard to improve on whats been said, go easy on the Clorox until you get just enough.