I’ve used purell to get sap off my truck. Of course that’s painted metal, and you don’t want to do in the heat of the day if you can avoid it. It may work for this as well.
What you do is put a small amount on the sap droplet in question and let it sit for a short time (a min maybe?) then using a soft cloth and gentle pressure just rub in a circle, rinse and repeat until it’s gone. I usually have a wet cloth to quickly wipe off the area right after as well.
The Purell has just enough alcohol content to get through the sap, and I guess the thought is if it doesn’t eat your hands it should be ok for this? I try to do it quickly because I don’t want to hurt the paint on the truck, but I feel like if a little purell can hurt the paint...might be something wrong with the paint lol.
So maybe try it in a more hidden spot and see what the results are like. Of course if you have a ton of spots or really big one this could take awhile.
Acetone would probably leave a mark as it might attack the coating. I would not recommend trying that at all. You could always try denatured alcohol which I think is much less harsh, or if you can find it, 3m bug and tar remover. I’ve been able to use the purell trick on road tar from recently repaired roads on my truck as well. I have never tried on the trailer though..never had the issue.