Ace your a star !!!
Yes while the greenhouse base is 10x8 i am having an additional 2 ft around this done in concrete as well and edged in brick to accommodate any movement and the risk of cracking. This is partly why the greenhouse base is going in now as February not great for setting it hard :)
But had not though about the pipe, yes good chance it will need power and water!!
Had also considered leaving a hole in the middle for a heat sink but have decided against this now as its going to be 2 risky that it would fill up with water and turn into a pond before the greenhouse is built.
Cam