Here is a suggestion on how to make a module:
If your target is light weight, strength,portability and durability consider using 1/2" Birch A-B plywood .
Have the shop take a 3' X 8' rip, a 3" X 8' rip and a second 3" X 8' rip that will supply your deck and two side frame members.
Then take the 3' x 8' and cut a manageable deck length like 5' for a 3' X 5' deck.
From the 3' x 3' cutoff have the shop rip five 3' X 3" cross members on 16" centers.
Predrill all cross members prior to assembly for wire management holes. Always confine all holes to the center third of any material.
Use the precision cut deck panel as an assembly pattern, lay out the side members and trim to fit, position the cross members and trim to fit.
Cut some glue blocks. Lay the deck on a perfectly flat surface and shoot it together with clamps and polyurethane adhesive.
Model Railroad Benchwork is a very reasonably priced company. I would consider asking them if they may supply a pre cut kit. Or even have them make the straights for you.
I would not think to use dimensional lumber for model RR bench work. No telling how the wood may warp. May be OK, may NOT be OK. 'taint worth the gamble IMO. Remember you are looking for repeatable R&R of the modules. You need dimensional integrity.
Also, think to request predrilled wire management holes for your curved ends.
Sample photos:
Tight bond for a clamped assembly or polyurethane for a brad shot assembly. Use corner glue blocks.
Add a bottom skin for an absolute rigid module much like a hollow door blank.
