Well, a lot of suggestions were offered, and I appreciate them. But I have only limited good news to report. Thinking the graffiti would be easy to get off with the right product or technique, we found out different after a full day of attempts. The fiberglass sleeper came clean but the truck body did not.
Part of the problem was that we were just beginning a long run when the graffiti was applied, and the route took us through the Mojave desert, which meant several hours of very hot and very dry air blowing down the side of the truck.
Another problem was the run itself; two days of non-stop driving that left no time to work on the "art" and gave it time to set all the more. It was a reefer run on which the reefer must run at all times. A truck wash stop was not an option as truck washes want reefers turned off when you are in the bay.
Third was the long weekend. We searched high and low for some of the products mentioned but the industrial supply stores that sell them were all closed on Saturday, Sunday and Monday.
That left us going to Home Depot and hardware stores to find one product after another, when each product we tried failed to do the job. The ones that worked, worked only to an extent; taking some of the graffiti off, but nothing got it all off. The truck looks better but to look right, it needs repainting.
We have two last chances; the Sprayaway wipes Turtle recommended, and the 3M eraser product fastman_1 and hondaking38 recommended. If we can find them after the long weekend, we'll give them a shot, but with the long time the marker ink has had to set up, I'm not optimistic.
In five years, we have never had a truck vandalized like this. From now on, we will carry a supply of graffiti wipes with us so we will be better prepared for the next time. Carry them in a cargo bin, not in the back. That way, if you need them when you are under a sealed load, you can get them.
Here is a summary of the suggestions and results:
Diesel Fuel: Tried, no effect.
Oven Cleaner: Tried, no effect.
WD-40: Tried, partial effect.
Paint Thinner: Tried, no effect.
Bon Ami: Tried, partial effect.
Goo Gone: Tried, no effect.
Gasoline: Not tried.
Goof-Off: Tried, partial effect.
Blue Beacon Truck Wash with acid and high pressure hoses held very, very close to the graffiti: Tried, no effect.
Oops! (product name): Tried, partial effect.
Aerosol Hair Spray: Not tried, but we will give it a shot.
At this point, we have nothing much to lose. And if the hair spray does not work, at least the truck body will not be too stiff or sticky, and it will have a style that looks beautiful and moves naturally.