Update: the removeable terrain boards show above warped a bit and wont lie flat in the tray anymore, so back to the drawing board for that particular tray.
In the mean time I purchased a smaller MDF tray, painted the bottom and flocked it. It is a bit small for 15mm games at squad/section level, but I think it would work for 10mm well enough.
The following are shots of a WW2 game in the making. Figures are Peter Pig, buildings are Red Vectors sold through Minibits, the trees are something cheap I based, and the hay stack is a work in progress that I scratch built:
As you can see, the second tray is too small for 20 figures per side in 15mm, as the game would start up in close contact with each other.
The first tray measured 53cm x 32.5 cm, whereas the second one is 37.5 cm x 27.5 cm. The 10mm figures fit ok on the smaller tray, so I may end up going with the 10mm for the small tray.
I am thinking of making a tray myself to get the size I think will work, but I am not much of a carpenter, so might have to think long and hard about that idea.