Clear Plastic Box As Cold Frame?

[salome2001]

it's nothing amazing, just three pieces of wire bent into semicircles, with plastic draped over it polytunnel style and sellotaped over the wires at the end. Not large, only about 1m by 50cm. The clear bags are the "LDPE4" type bags you get in IKEA flatpacks.
I only really need it to last for a month or so until the frost risk is over.