Permanent Mulch idea

[jcrous]

I am now constructing my polytunnel, which will be finished soon.
I am planning to plant in 25 L / 5 gal pots. My medium is a basic soil mix of 60/40 Compost / Soil.
In the very hot climate of Cape Town, I must water daily or my plants will die. I get blossom end rot in the containers, but not in my soil beds.
Not enough water is partially part of the problem. I work during the day, and can only water late afternoon.
I am now considering mulch, but I would like to use a permanent mulch.

I am thinking of making a disc of plastic, with a hole in the centre and a slit halfway through. I can also use multil-layer discs of 100% shade cloth to breath.

Any comments or better ideas? Possibly a link to similar posts.