Are they leaking before the valves or after?

If you are using the black polyethylene pipe as the mainline, or the line under constant pressure, you'll never get them drip tight.

If they are only slowly dripping, and not actually running water, you may want to install a master valve at the water source, plumbed in pvc and wired into the master valve or pump terminal in the controller, which will only pressurize the mainline when the controller turns on a zone.

Tom

Never been a fan of wormgear clamps myself, IMO the Oetiker crimp type are the only way to go; and always doubled up. I wouldn't recommend using poly as an always charged mainline, at the very least install a master valve as previously suggested.

Are you heating the poly to ease the installation of the fittings? I dont recommend doing this, some folks do, if you do just dont over-do-it as it can result in deformation of the pipe to an extent that makes it very difficult to get a good water tight fitting.

All that said I cannot imagine why you are having so much difficulty as poly is really pretty easy to work with and get good tight joints.