Playing around with a netbook, and not feeling like playing with ports or reading, I made the nice discovery that dwm will just build on OpenBSD. In other words, downloaded the source code, made my changes to config.h and patched with a patch I like (to resize floating windows) ran make and it built.
So, for the lazy person, that's probably the easiest way.
I only dabble with OpenBSD, and custom configuring dwm would be the only reason I'd be using ports--otherwise, just about all of their defaults are fine for my needs.