We took the Velcro method and changed out the Velcro to use a bungee. No more attaching Velcro or having Velcro wear out. Just add a loop to the end and fish a bungee through, hog ring the ends together and be done for the season. Video of a one person change here:
http://www.youtube.com/watch?v=XYTiRxLw7oA
I have already had a request for a how to, and I will post a white paper when we build our bumpers next week.
We also use t-shirt vinyl and a vinyl cutter to create our numbers and then heat press them on.