Long story. I saw Andreas Hatveit's candy invitational edit from last year and he had a lit up fun box. I wanted one, but his looked like he had found some clear hdpe and had the lights inside the box.
At first I found out that they make clear PVC. I thought I could run rope lights inside of the clear PVC pipe. I found out that it is like 10 times more expensive than normal white PVC. One clear PVC pipe was going to cost about $30.
The way I made mine was to use 1in white PVC spaced about 3/4 inch apart and I have the rope lights running between the PVC. The gap is wide enough that the light from the rope lights comes through really well and makes it look like it is a lit up HDPE surface. The gap between the PVC pipes is still narrow enough that my 8 year old son can 50/50 it just like a normal HDPE fun box.
I bought my rope lights at Ace Hardware. They are like $10 a piece and I think I used 4 for my box which is like 18 inches wide and 10 feet long. I used solid blue colored rope lights on the edges and multicolored in the middle.
If anyone wants tips on how to make one of these, I can give more details.