Local big orange shed had some surprisingly decent 5.5mm nominal ply in stock, and have cut it into 400mm strips for me, two 1200 long for the main board, four 900mm for two extension/fiddle yard boards, the off cuts will also allow for a 335mm extension for use with the main board at home, enabling runaround at both ends.
My thoughts so far are to form each board from a giant L girder formed by two sheets of 400mm ply, giving an integral backscene, with the track bed raised up on 50mm Knauf foam boards. These will give rigidity without the need for cross bracing, and raise the track to enable a dockside feel. At the moment these might stay at 300 mm deep, leaving a lip to be sceniced as the water in the dock.
Still to be resolved before construction begins-
How to join boards (split pins, sprung latches, clamps?)
Do I need a subframe to enable underboard wiring, or do I bury it in the foam board.
Legs - do I attempt to incorporate integral sockets at the rear of each board.
It's probable that I will drill lightening/access holes in the bottom board. Do I do these cookie cutter or one single picture frame style?
I'd like to keep the line of the backscene at the rear of each board - how then do I access the staging tracks?
Electrical connections between boards can be by way of banana plugs on the bus wires.
What else do I need to consider? And what have I completely forgotten?