We want to make a Cloche with hoops of bent-over plastic water pipe, covered
in Plastic sheeting; to end up like a minature Polytunnel for the allotment.

We dont know where to get a large sheet of plastic from here in North West
London, so we are going to stick together 'cut-open' clear plastic bags.

What would be the simplest way to stick the bags together, and if glue is
the answer; what is the best type of glue to use please? Bearing in mind we
would probably have to use lots of it and it would have to be one hundred
percent waterproof. Thanks.