OK, I have the OTA together & it is all working. I realised I made the dew shield incorrectly once I saw Bill's comments. It needs to fit further down the cell over the flanges & not at the end the way I have it.
Oh well, first you make it then you fix it.
What are everyone's mounting ideas? I was thinking maybe just a camera tripod (it is 1.6kg), or a refractor dob mount like the one in Richard Berry's "Build your own telescope" (with round dob alt bearings on the sides). Ideas?