I don't have any experience with RPM, but to build a package for a reasonably big part of the Debian-based world, you have to set up a build system (pbuilder/cowbuilder) and tell it something like `for DIST in lenny squeeze wheezy sid lucid maverick natty oneiric pangolin do; git-buildpackage ...; done`

The problem is, to get it right one has to find and read TONS of documentation.