So I make my own....
Step 1: Thinking about it....
I realized I just needed a 10" piece ... after check my macbook, which measures 12 " wide and I decided to leave an inch free on each side.
I think you can use a PVC tube instead of aluminum.
Step 2: Other materials: Rubber.
Cut only five very small pieces ... two 3 / 4 "square and three 1 / 4" by 3 / 4 ".
Step 3: Making it.
Put the two largest at the same height on one side of the tube. Fig 1.
the other we have to put them on the opposite side of the tube as shown in fig 2
Use masking tape to hold parts in place.