At the risk of being a bit controversial there seems to be view that Depron is a poor structural foam.
Surely the important issue in any airframe material is its strength to weight ratio, both in tension and compression.
As a plastic foam Depron actually has quite a good strength to weight ratio and importantly it has a surface 'skin' as well. In addition with the right glue a joint can be virtually as strong as the material itself.
So if you keep within its stress limits and retain its skin surface you can build quite complex light, strong, rigid structures with a smooth surface.
Not a bad receipt for an airframe!
To test this I made a simple 40" wing in 3mm Depron but using a conventional built up 'rib and skin' structure to replace a solid foam, part reinforced, original.
One advantage of using a relatively thick wing skin is that it does not need so much support for it to take compressive loads.
The servos were built in making use of the ease by which Depron can be cut and glued.
To keep the surface skin intact at the trailing edge the top and bottom wing skins were sanded on their inside edges prior to being glued down.
The final result was a wing with a good Clark Y profile and a smooth waterproof surface.
To complete the structural test the two wing halves were simply butt jointed together!
Nearly 50% lighter, just as strong and in aerodynamic performance a whole order better than the rather crude 'moulded' foam one it replaced.
Maybe not every bodies 'cup of tea' but to me the opportunities of Depron seemed considerable.