Jim What is your argument against double wall with sand ? is there a technical disadvantage apart from weight? If I use 1.5" MDF vs 1/2 MDF 1/2 sand 1/2 MDF I calculated that I would have about 15 Kg more per enclosure on a total weight of 90 KG before sand ! of course the bracing is intensive , eight horizontal sheves one between each driver, but depth is 41 cm , should I divide the depth too or would angled corners 2"x2" do the job? JP