The SkyShed Pod supplier recommends Lexel. It works reasonably well with HD polythene which is more or less a non-stick material for adhesives. I’ve found it very good. It’s a bit expensive and difficult to find.
You could try:
http://www.repairingproducts.co.uk/product/lexel-13013-sealants-lexel-adhesive-caulk-5-ounce-clear/