If there?s room, I recommend using the M19?s 30? o.d. width x 21? o.d. depth.

Yes, as already noted, tube ports are the way to go if they need to be longer than baffle thickness.

I wouldn?t have recommended the MLTL if I didn?t think it a good option. Don?t know your average seated ear height, but ~38? is common, so adding half the horn recess height + ?? top plate = 43.5? high, ergo using 19 mm BB, Apple or marine grade no-void ply it for sure won?t be light, but nowhere near 300#.

The Stonehenge tower is what we now usually refer to as a MLTL, but from an acoustical POV, not a particularly good one since it retains a BR?s ~ideal vent location, i.e. as close as practical to the driver.

This not only defeats the cab?s TL modes vent damping ability, but also adds a notch in the mid-bass right where you don?t want one and last, but not least, causes some amount of peaking at Fb that when placed near a boundary can color the bass too much, though of course it can be damped down with additional stuffing if need be.

Spacing speakers up off the floor can roll off the bass too much and vertically ?gapping? the woofer/horn can cause audible phasing problems if the listening distance isn?t far away enough for them to sound as one, so best to have them as close together as practical, especially since you?re doing the XOs digitally and don?t have to worry about the delays that passives have.

GM