On 29 Apr, 13:50, pete wrote:

How about sun reflecting paint?http://www.wickes.co.uk/Solar-Reflec...ing-Paint/invt...

It's not something I've used myself, but it gets some good reviews.

It's usually better to fit a "safari roof" (old Land Rovers) and make
that into the reflector. A sheet of something spaced about an inch
outside of the main roof, with an airgap beneath. As the safari roof
doesn't have to be waterproof, it can be made simply without having to
seal the gaps. Metal or Versapanel will do.

I'd think hard about a green roof instead, with an inch or two of foam
insulation between it and the container.