Lip on Blind 2. "It's not about how it looks, its about how it feels. Thats a larger message to be applied across all of skiing. If you're skiing for looks then you aren't skiing for yourself." -Tall T Dan
The smaller diameter pvc pipe you use will make it less likely to catch an edge but will also cost more... Try to find a happy medium - I did 5x2" dia for a 10" wide box that was kinda sketch - I would recommend using 1.5 or 1" diameter if you can afford it.
I know this is a little late but at menards they have these like 1/4 inch sheets of HDPE and I really want to try it out because it looks like it would slide well. So if you haven't already built a box maybe you could try a sheet of that and you would be able to build many boxes with the 4'x8' sheet of it.