I would wash first with an RV/boat gel wash for Fiberglass and then polish with a boat/rv cleaner wax like Maguire’s #50 cleaner wax applied with a griot’s garage random orbital polisher and a red waxing pad. After the wax/cleaner dries remove with a microfiber towel.
Tire dressing like Maguire’s Hot Shine will fling off if not fully dry causing similar spots.
2014 F150 SCrew 4x4 Max Tow Heavy Duty Payload 3.5 Ecoboost 6.5' bed Ingot Metallic Silver
2015 Rockwood Roo 21SS