I used
BSP Viewer. The same author released a newer version called
Crafty, but I haven't tried it.
Another one is in Botman's
BSP Tools package. But I haven't tried that one either.
I only used them to get the general location and size. It was trial and error after that. But it looks like Pixie has an interesting idea going on. Give that a try. It sounds like a lot less work than my way.