A note, since it may help some of y'all... I've come across a couple articles on glues and the like recently and figured I could share.
For this type of work, good old white Elemers all-purpose glue may be the best choice! It's the same stuff as the yellow carpenters glue, with longer drying time (more room for you to fidget) and no yellow die - it dries clear. However, it's thinner which makes it less useful for filling gaps and for general carpentry (where it was designed to be used!) For fine, close fit joints (cabinet-making, and the like) the white glue works great.
Gorilla glue is a completely different type of glue, and may actually have a weaker bond when working with MDF. It's designed to be used where weatherproof is key, and it needs some moisture in the wood to really bond as well as it can.
For J. L.'s sonotube issue, I would have pondered through-bolts (much like retaining wall anchors work) or, as he did, not use MDF.
Though, I'll be installing an IB manifold sub. Strong response to 5hz just tickles my fancy for some unknown reason. And, of course, opposing drivers mean any big forces end up being cancelled out.
I need to find a good built-in speaker solution though. (This, for a home-theater).