This image shows the internal construction. I have been very liberal with glue and sealer as I had two cartridges that would dry out if I not used them
I bought some fabric in a style that is typical of the time period 50 years ago when the Trike was concieved. I picked a eleastic fabric and sewd it as a tube that was pulled over the pipe more or less as a sock. Then I used a staple gun to fix the fabric at both ends.