How to secure/fit poly pipe over raised bed for shadetunnel

I don't use them but your oarlocks suggestion seems good.

Seriously though, you can put a couple of holes through the pipes at each end and screw them to the body of the bed or alternatively, sink a length of steel rod into the ground at each side and slip the pipe over. The stuff used for concrete reinforcing should be ideal if you can get your hands on it.

You will probably need a rod of some sort fixed to the top of the arches to stabilize them or they will have a tendency to flop sideways

Hmmm....

I like the pipe idea. I'm thinking I might be able to use some galvanized 'sleeves' for the poly to go into, and can secure this to the side of the bed with some galvanized U brackets. To stabilize the tunnel I guess I will have to use some lengths of poly fixed in to the main arch, horizontally at intervals.

Here is said bed. Has been a bit of a palaver to build as I've used salvaged lumber from an old shed I'm pulling down, and nothing is of equal lengths/widths. I'm at the point now where I have to level it off and put the rails on. 12 foot. Lot of work with the jigsaw. I'm about 75% happy with it considering its cobbled together from Junk, and it will look nice once it has been sanded and hit with some decking oil. Striving for mediocrity in a world of excellence. Wood isn't really ideal as a material here in Queensland, very, very hot wet and humid in summer. Aussie hardwoods aren't as good as the English kinds either, ours tend to warp, split and rot more easily. But it was mostly free--and I like free.

I'm not sure if this what you mean but I'm using plastic clips that are used to fix the pipes in the wall. If you get them from Wicks they come with the screws if you get them from B&Q you get more without the screws. I also use them to stick the enviromesh or fleece to the pipes and they are easy to hock and take off.

Wickes Black Solvent Weld Pipe Clips 32mm (Pack of 2) | Wickes.co.uk

This is how it looks in my beds



Hope it helps.

For another variation, I simply banged in some 6" nails where the hoops were required and the netting held it down, the netting being pulled over short cement nails that are placed every 6" around the base.