I’m a complete newbie to all of this! I have lovely memories of “being in charge” of my big brothers train set in the 1970s, but was never allowed to have anything like it as a mere girl.
As my husband has always wanted a model train set, now is as good a time as any, and we’ve decided to have a bit of fun making landscapes, models & buildings to make our new interest even more fun.
We’ve set aside a spare bedroom (which is tiny) but it’s just about large enough to have something about 8ft x 4ft (2440 x 1220 in new money
) and have got a carpenter coming to build the platform (baseboard?) for us to start during the Christmas holidays (we’d do it ourselves, but it would be wonkier than a slalom slope 
) and would appreciate and advice or input .So, the baseboard - 9mm ply, single sheet?
Legs, a PAR frame, free standing, supported at 600 centres, do we need to brace? The ply will be screwed to it. Height to be decided (argued)
Sealing? Advised or not? We we have some fairly interesting & ambitious plans for landscaping (hills, vegetation, tunnel) and don’t want to do anything on the surface which might cause bowing.
As I say, we are just starting out, and we’re a bit slow, but really want to get the base right.
Thanks in advance
. I have no connection with MRS - but they are good and helpful. You mention 8x4 if that is one sheet, you will have difficulty reaching over four feet, unless your room gives to access all round. My layout is in the "small bedroom" 10x7 and the boards are two feet wide running around three walls - it's an end-to-end layout rather than a circuit(s). 