simy1,
thanks for sharing your experience.
What would you think of a ridged frame for the tunnel? I'm thinking more
pvc across the bottom with Ts and rt. angle connectors to tie the bottom
of the tunnel together.

I don't have the mechanical problem of snow. I'm on the hilly edge of a
redwood (temperate rain) forest. When the wind howls on the flats around
here, we have a nice breeze. It can get windy but not extremely. Our
problem is that these humongs trees don't have tap roots and when they
come down (not if), they can slice a house in half like a birthday cake.
Fortunately, I am surrounded mostly by oak and bay. We get about 40" of
rain between Nov. and April. The temp may drop to 28F on occasion. I saw
frost four time last year, which is typical. Lastly, the Sun doesn't get
above the tree line from mid Dec. to mid Jan. During the summer, the
sweet part of my garden gets about 6hr/day of sun (the rest of the
garden gets less as it goes down the hill) and the temps are typically
in the high 80s.

Anyway, my thought is with a stiff frame, about 20' long, I could undo
the ends of the frame and one side and open it like a chest. Do my
gardening and then just re-dress the three edges. I'm presuming that
larger chunks of concrete or cinder blocks can compensate for the
inherent aerodynamics of the tunnel. I'd love to hear any thoughts.

I do get some detritus falling off the oaks and bays. The largest are
small limbs (1' - 1 1/2' x 1/2") that are totally rotten out (fairly
light). Can you quantify or qualify the strength of the vinyl?

Is there any problem with humidity in the tunnels? Do you ever have mold
or mildew problems?

Gratefully,
- Bill