There's a rubber wheel that you attach to your drill. Looks like a gum eraser. I used it on my old RV and it worked pretty well, but used more than one. I found it at a auto parts store in town but you could google it.

they sell a commercial decal remover.......

www.beacongraphics.com/supplies/vinyl-off.html

What about something like Goo Gone?

When I had bought a stacker trailer it was loaded with decals of the racing team name, etc. I let nature help me and it worked great in my situation. I just parked the trailer with the side facing the hot sun.......Peeled off like nothing. The only thing with the sun shining on the bright white trailer I had to wear sunglasses and lots of sunblock.
I also have a commercial style decal remover from MAC TOOLS. Air powered and the eraser wheels are like a gum rubber and look like a tractor tire. When used correctly they can remove stubborn decals quickly and easily.

Thank you for everyones input. I am excited to use the eraser wheel. Did not know that they made such a wonderful tool!