To remove any type of adhesive or oil, be it glue, tar, sap, grease or any other sticky nasty thing, I use orange oil. Now you have to be really careful about what types of plastic you let a citrus oil come in contact with. It will melt some of them. I have used it on my Scamp
16 with no ill effects.
Here's what it looks like. I use Pure Citrus brand as it is literally only orange oil. You could mist it over a cake if you wanted with no harm. The oil is stored in a pouch inside of the can, so there isn't even propellant in it.
It's the least expensive at Home Depot at only about $2.99 a can. It is amazing as an air freshener as well, so it's really multi use. Oh, and to add another amazing use; It KILLS bugs DEAD. Like nearly instantly. It's like a super fly swatter that can take them out mid flight. But again, be careful where you spray it when near plastics and paint
For mechanically removing things from the trailer I love to use Magic Erasers. I buy the off brand ones from Dollar Tree. Much cheaper than the Mr. Clean brand.
If you've never tried one you should. Some care must be taken though, as it is essentially an extremely fine abrasive. So fine it will polish most things, but may frost some clear plastics. I've yet to have that happen, but just beware.
To keep such nasty stickies off of your trailer in the future you could clean it well then coat it with floor polish. Works great, looks great, and things rinse right off without leaving stains.
Hope this helps!