Simplicity and affordability were the constraints in building the tunnels. We designed them to mimic low tunnel construction used outside: bended hoops covered with a layer of plastic. Indoor construction on benches involves a few more parts, but they are commonly found things and are cheap. We used only these seven parts:
1/2" PVC pipe
1/2" metal brackets
The greenhouse benches are made of aluminum and are 10' x 4'. So, the first step was screwing the brackets on using the tech-screws. To ensure the pvc wouldn't wiggle it had to be placed in the bracket as it was being screw on.
Each bench used three pieces of pvc: one for each end and a middle piece to keep the covering from sagging. The coverings were attached to the pvc using 1/2" snap clamps from Johnny's. These are the best and made building the tunnels really easy. They come in four inch pieces because they are designed for outdoor use. Since these low tunnels are not outside and blustery winter weather won't be an issue we cut each one into four smaller pieces. From 40 snap clamps we ended with a big box of 160!
Each low tunnel was covered with three pieces of material. Each end-piece was attached to the pvc with clamps and to the bench with binder clips. (Since starting this project I now have binder clips in all of my pockets.) The largest piece of material is pulled tight over the low tunnel and secured to the bench on only one side. The other side is attached to a piece of pvc with more snap-clamps. The weight of the pipe holds this side of the tunnel down and allows it to be easily rolled up.
To get the rolled up side to stay up I duct taped a bike hook to a snap clamp and put it on the central piece of pvc in the tunnel. So far these have worked really well, although I am careful to unroll the tunnel side and not just let it drop in case the hook could puncture the covering.
Next up: low tunnel coverings!