because Im teaching my daughter on one of my super wide boards that aren't easy for her to carry, I thought I'd have a crack at making one of these yesterday arvo.
I had some 5/16 copper tube (3/8 would have been better)
A 3/8 bending spring (now you know why 3/8 would have been better)
Some mapps gas to anneal the copper tube with (it was Pre-annealed, but that was 20 years ago, minimum)
a length of styrofoam insulation that was originally covering some sort of rod for a babies play pen.
A stick of silver brazing rod, because I thought there may be enough copper to do a continuous loop and join it end to end (there wasn't)

Once I annealed the copper, I got all the old bends and kinks out of it. then using the bending spring, I eyeballed a few curves to suit my extra thick rails and covered the tube with the styrofoam.
Then I found an old bag strap, cut it to length, sealed the ends with the mapps gas, doubled them over and using a soldering iron, I cut holes through the the doubled webbing to suit the tube, and seal at the same time.
Then I threaded the copper through the holed, flattened the ends and bent them over to hold the webbing.
Seems to work and the daughter was pleased when she used it today because we needed to park a long way from the beach
I reckon those store bought ones would work much better than mine, but you know what I'm like, I get really bored and just like having a go at things.