A simple LINK module was constructed one afternoon using left over 1/4" plywood. The module is just under 4 feet long. The interface plates are 12" wide and the sides bow out slightly to about 16" near the middle.
Here is the bottom with access holes removed.
1/4" cross members and 5/8" ply subroadbed were cut to size.
Here's everything assembled and glued with a bead of construction adhesive along the butt joints
After an overnight wait for the glue to dry the finished frame is ready for track and scenic treatment.
Construction time was about 3 hours.