We bought on of those Gardman plastic Greenhouse/polytunnels about a
year ago.

Those familiar with them know that the entrance is two full height Zips,
just like on a camping tent.

The Zip is broken and was never really strong enough to be up to
repeated use.

Would anyone know of any kind of fastener i might replace the Zips with,
hopefully keeping as much as the warmed air in as possible when they are
closed.

I'm not inclined to, or skilful enough to sew in another zip and the
only thing i can think of so far is about half a dozen adhesive backed
Velcro strips place horizontally.

Grateful for any other suggestions..... thanks.