As long as I’m thinking about module designs in a general way I should pay some attention to the interface plates that serve as the mating surface between two modules.
Interface plates should provide a way to roughly align one module with another. They should also either provide the clamping mechanism that securely joins one module to the next or it should provide a suitable surface for an external clamping device.
Probably the most common way of fastening one module to another is the use of C-clamps on the interface plate. Now C-clamps are probably not the ideal choice of fasteners for a number of reasons. If we assume for now though that the fastener of choice is the C-clamp then you do not want to use a soft wood for the clamping surface. Pine and even most hardwoods would soon begin to have clamp marks that begin to interfere with proper clamping after awhile. For this reason, a good birch or mahogany plywood is the first choice for wood interfaces.
The interface plate needs to be sturdy but the main reason to use plywood is to hold up against the ravages of C-clamps.
The obvious question. Is there a better fastener than a C-clamp?