I want to patch on Trac package. I know how to patch and rebuild the package, but there are some things I don't understand very well.

My patch is something dangerous and not likely to commit back to the community. So, let me just say, it's a very private patch. But, I want my patch keep working when the Ubuntu packages upgrade. (Should I apt-get source trac and move my patch to the new version of source directory each time the Trac upgrades?)

I see there is a patch/ directory (many using quilt I guess) in debian/, but I don't know how to use it? Will debuild automatic apply all patches in the patch/ directory? And what about dpkg-buildpackage? Is there some environ variables to control the selection of patches to apply?