You need, or you think you need? A few pages back in this thread there's "jo bg" using Cubo Kick 15 with 2 kW sub bins, with ease. But sure why not, I might even design a 21" kick one of these days. It would help, if you told me what drivers you're going to use (or if I can choose). Low Qts, low to medium Vas, neo drivers are easiest to implement.
@Ip8124: I'm planning on increasing the depth to 65 cm. If you're satisfied with a finished Sketch-up model (and work the rest out yourself) you could have the model before the end of the year.
@Mikelink: I'll be working at a Sketchup model of the trap version of Cubo Kick 15 and Cubo Kick 18, for the coming month. After that I should have room for developing Cubo Kick 12, remind me by then if you're still interested.