Scrapped original idea in favor of simplicity and time. I'm going to bond together 1/2" pink insulation board. Since it will be covered in carpet, this should be sufficient. I'll add a few glass strips around it and where the mounting hardware goes for strength. Initial weight indications are that the sleve will weigh about a pound (not counting the bracket). Since it is so light, I'll make one for each side (ELT antenna in the middle).
