Can I create a preset BSP brush?

Clicking in the Modes window and clicking on BSP, it gives you the list of different shapes you can drag out and begin working on. But what if I want to create a subtractive brush that serves as a doorway blockout, but I get tired of always dragging out the Box brush and resizing it every single time (or having to always find another doorway and duplicate it)? Can I create the preset brush that I want to use, and then save it under the BSP menu or save it elsewhere so I can just drag out that specific preset and place it easily?