I think its overengineered with the paving and blocks most people will just plonk it on top of soil and leave it at that which also brings me on to the shallowness of the compost most people would simply rotovate and plant directly into the soil root veg will need a deeper soil and it'll likely dry out quickly but good on you for making the effort.
Will it need heating once we’re in the worst of winter?
It's not practical to heat anything other than very small greenhouses and even then only if you were growing some sort of exotic that you want to protect. Polytunnels feel warm even in the winter because of the reduced air circulation. A trick people use is to put large water barrels in the polytunnel to act as thermal inertia, it slows down the loss of temperature over night. I think you're hardy greens will keep on growing in in the winter for most of the UK. First tunnels have some excellent month by month advice cards for tunnel users. HereWill it need heating once we’re in the worst of winter?
Any fruit planted ? Was imagining grapes hanging from the roof
You may find the lettuce isn’t what you expected but don’t let that put you off, I would suggest you may be a little late in the year to have it in the poly tunnel, it tends to go bitter when it gets to much heat but still looks just fine to the naked eye, I try to finish my lettuce crop in the greenhouse sort of mid may and then move to outside (still start the plants in pots in the polytunnel just don’t plant them inside).
Any fruit planted ? Was imagining grapes hanging from the roof
Will you be getting any sort of temperature control, automatic vents ?
Lettuce Update….
Was delicious
What are you growing in the pollytunnel altogether?? Any Brassicas in there??