Tunnel construction problem - your thoughts please

I intent to build a tunnel the same as this and cover it with net

http://www.overthegardengate.net/UserPages/pp_view.asp?FName=polytunnel&Page=1

He has used 63mm pipe which fits over the top of the scaffold pole but the problem is is that the 63mm is very expensive   and its doesn't seem to be the sort of think you see lying around.

So my question is do you think i would get away with using 32mm pipe which will slide inside the scaffold pipe and is a quarter of the price  .  I thought if i spaced the loops at 4ft instead of 5ft it may be strong enough.

What do you think.
Cheers Chappers

We have used 68 mm black pipe which was lying around  , but yes I understand that 32 mm is deemed to be strong enough for most situations, especially if you cover it with netting and shrink down the loop spacing too.

Yep, just to keep the butterflies off  . I have some 2m wide debris netting that i intend to use around the side, and then the top will be covered with butterfly netting which i thought would let in more rain.

Chappers