Thank you for all the replies!

I have a site setup its the south side of the greenhouse running down
the east west direction that the greenhouse also runs. So its getting
as much light as it can. I was presuming that because of this I could
do things like have a more solid back (the north side) and maybe even
sink it down slightly maybe this would help with keeping in the heat? I
guess you could also put over bubblewrap like used in the greenhouse on
colder nites?

There was something on TV once about someone using a white base to
their polytunnels and the differences in the plants was massive. The
ones that were on the 'normal' capillary matting were taller and less
bushey.

I have also found that if you can remove the top of the frame it makes
cooking less likely. I am also going to have another one in another
aspect later on for other types of plants.