This is a great advertising opportunity, use a Changeable Transit Banner System.
We’ve done this truck for about 5 years with this system. They update the marketing for current specials or promotions and/or advertising campaigns. Here is a link over to when we originally did this truck.
We even added permanent vinyl lettering under the banner area if they wish to use it without a banner.
If you have a box truck are your using it for your maximum advertising opportunity?