I think I'd opt for foam over plywood in any condition. The form allows for minor contours (drainage ditches, etc), while the plywood gives a firm base for attaching any under the layout paraphernalia (like switch machines). Thickness depends on topography. If you terrain is supposed to be "flat" (my modules are flat - East Coast urban) I can't see where foam thickness matters. I'm building 2' x 8' free-standing modules on 42" legs. (I plan on moving some day). I used 3/8" plywood with 1" foam on a 1 x 4 frame. Before gluing on the plywood, I painted all the woodwork (legs, braces, framing and plywood) with a latex paint to make the wood moisture resistant. None of it will be seen when I install a fascia and skirting, but the paint store had some custom mixed tan roughly the color of the wood that was real, real cheap, so mine is painted a custom mixed tan that's roughly the color of wood.... (I may have been lucky - light color makes it easier to see what one is doing when working under the layout). Ask me in 5 years if it worked, but it should. It was a belt-and-suspenders collection of the recommendations from a number of different sources....
I was replying to the post just before mine, but after re-reading it again, I don't remember exactly what I was asking. Cheap, flat white paint ok?
I use a "sandwich" of 1/2" plywood, 1" foam, and ceiling tile (upside down - measures about 5/8") ---- this gives me plenty of rigidity, plus I can cut in all the scenic areas I want. Ceiling tile works really well, as it takes the nails I use on my Unitrack really well & holds well......also takes scenic glue exceptionally well, just don't get it sloppy wet - I seal mine with a coat of paint before scenicing.
I use Unitrack, and attach it to the ceiling tile with long brass brads before ballasting, which the ceiling tile holds tightly. The foam is used to thicken the "scenic layer", that way I can cut in creek beds, washes, cuts, etc. deeper than the ceiling tile thickness if I want to and still completely preserve the integrity of the plywood base.
Cheap is the important part. I suspect think lighter is better because it makes what your working on under there easier to see, but there may be folks who've used dark colors and had no problems. Anyone?
I would figure primer or flat white latex paint, but; if I use foam over ply, why would I have to paint the plywood at all??
Replace 'em. Two tubes, even top notch color spec'd ones, will cost you less than a pair of decoders, and probably be a lot easier to install. Don't toss the old tubes, just keep 'em around as spares for when a tube somewhere (garage, utility room, or layout) goes out.
The lights seemed to work out fine. I just wished the dimable function would take the output down more than what it does. At least they aren't power hungry incandescent. If it was a larger room with a higher ceiling, tubes would probably make sense. But it is neither.
Ken- Four decades, four years, four days, or four hours. It doesn't matter. Hank is the only person I have noticed who lines up the four screwheads that attach the facia on the left side of the second photo. OP- If you are looking for a lot of contour, go with 2" foamboard over plywood. You will then be able to dig down as well as build up without going subsurface with cutting up the plywood if that is what you are trying to create in a particular scene.
You already have the plywood. If you are stuck with it use it but maybe not for the top bench work. I definitely encourage foam for the top layer. As for workbench design keep in mind future storage space: You might use the plywood for shelving under the layout. Um, but as for the smiling female assistant? you are on your own. Note: I had different parameters: It is in my dining / living room It is across a large set of windows and had to be movable in case access was required, (which it was less than 5 months later). It had to have storage
I decided to go foam over ply. 1/2" foamboard over 3/8" plywood. The foamboard was half price (2nd's). I don't plan any mountains or valleys hence the 1/2" choice.
