Steve,
MDF weighs 48 lbs ft^3. There's about 2.5 ft^3 in the shiva enclosure. So there's 125 lbs.
Add in a driver at 13 lbs, and you're at 138.
Add in a plate amp at 12 lbs, and you're at 150 lbs.
Figure another 5 lbs for ports, screws, glue, and paint, 155 lbs.
You'll have to figure out the aluminum on your own.
Chris
Not to butt-in, but on the aluminum cladding thing.... I would HIGHLY recommend a constrained layer dampening method of boding the aluminum to the cab AND use a panel press to make sure you have a 100% void-free bond.... Vac bagging would be even better.... with a low-viscosity, slow-cure gluing system... Otherwise, I would suspect that you may have some serious noise, vibration, ringing, et al... Aluminum can become very "musical" when excited...