My first foray into extension speaker cab: radiata pine, appx Princeton dimensions. I wanted a cab that I could easily install and take out speakers for break-in and testing with my amps (pulling baffles and/or reverb tanks on my PRRI and DRRI is not fun). After watching a few Youtube videos I took a stab at a finger joint jig on my table saw. After 4 fine adjustments with feeler gauges and still not getting a joint that would seat across 9" I threw in the towel and went with a dado joint reinforced with a corner blocking, plenty strong. I also have a new appreciation for anyone who can stretch grille cloth and get the lines to stay straight. At any rate, it's serviceable and I built a little tilt back leg for it. I went with Fender dimensions for height and depth (even the 1.5 degree taper from bottom to top) and 5/8" thickness. Next time I'd probably go a few inches wider for breathing room. Not ambitious enough to venture into tolex, I opted for a quick catalyzed furniture finish.