Don, your bride is very talented , and your trailer Very Nice ... (JMHO)

We have lots of trouble with mold and mildew around here too and the only thing we’ve found to keep the nasties away was a good washng every now and then ... And we’ve had to use Bleach ( diluted) to get the mold stains off ... We tried household Vinegar which seems to kill the mold but does not take away the stains like the bleach solution does ... so we spray with the Vinegar first ( garden sprayer , then wash with the bleach ... That works well ...
Also some UV and Mold resistant coatings ( clear ) are available commercially and we’ve used them in the past , Might bea good thing over the artwork ... ? We have used them on outdoor signs we made and it seems to protect for a while , but needs recoating after several years ...
Best thing we’ve found is to keep the trailer in the sun ( away from trees) , and park it end for end once in a while so the Sun gets to both sides ... Around here mold and fungus only grows on the North side of the trees , out of the Sunlight...
Never tried zinc strips before ... Interesting ...