Its been a LONG time since I posted on this, and the old thread is archived somewhere..
I basically binned the original 2 foot square boards and started again.
The new boards are 450mm x 450mm based upon 18mm Exterior Plywood.
I'm using the superb Fenris Games Sulacco tiles as a starting point - 450mm x 450mm allows me to have 11 squares across each board, with room for a 5mm wooden baton to protect the resin tiles from wear and tear.
As you can see, I've been hoarding quite a few of the tiles....

I'm then going to build the walls up starting from a 3mm foamcard core...
Fenris have left a flat border around the squares and I believe that Ian will be working upon some walls of his own - I plan on using the extra space to build up some alien gunk, plus use some other resin pieces I've been hoarding.

Dropships: Konami (diecast 1:72)
APCs: Galoob Action Fleet (1:50)
There will also be some upper levels, as with my previous project, and some ventilation shafts.
Rules will be homegrown of course!