The tubes are what window tinting is supplied on. You can get them for free from tint businesses.
The plastic bases are the ends that the tint (or vinyl) tubes roll on inside the box.
These M6 x 13mm threaded wood inserts were from eBay.
The M6 threaded feet were also from eBay.
I used some left over 10mm ply, cut a little larger than the plastic base.
Drill a 9.5mm (3/8″) hole in each corner, making sure it’s within the hollow space of the tube base.
Drive the nut inserts into the ply using a hex driver.
Drill a large hole in the centre for the cables to exit.
The screw in feet allow the base to be angled for use on a sloped surface (driveway, etc).
Drill a hole in each corner of the tube base, avoiding the areas where the nut inserts are.
Use 35mm 8 gauge screws to secure the tube base to the ply.