Good thought.Were you thinking of as permanent decal or a magnetic one that you could put on for events, but take off for day to day driving? I would like to have one to for trail riders and trips, but not sure if I would want something that big on the side of my junk full time.
A magnet is the way to go, but if you are a lead vehicle in a Overland Bound trail ride or get together it would be sweet to have.I have a Deadhead sticker in the back window of my LX (my nod to Don Henley's "Boys of Summer") but I can't see putting decals on my vehicles, especially large ones unless I drove a commercial vehicle and was advertising my business.
You can have them made at many sign shops. I plumber I know had them made at a nearby local Sign-a-rama shop (https://www.signarama.com/products/magnetic-signs). Staples and Office Depot/Max offer them as well.Overland Bound vehicle door decals, like some businesses use.
How difficult would it be to make?
I'd rock some large yellow/gray OB decals on my front doors.