New version to try
I have checked in a new version of InstaDMG into SVN. The changes is not all that big in terms of lines changed, but it has changed in one significant way: the upgrade packages now install inside chroot jails. This means that some of the problematic packages out there might now just work. This is especially true of installer scripts.
I am still working out all of the kinks from this version, but I would like to get more people to test this out. Thus far I am finding mostly changes that are improvements on my old images (odd corners seem to have not gotten previous updates), but I consider this all very experimental.
So if some brave souls would be so kind as to download the latest SVN version (188), try it, and report back that would be great. If you are not comfortable getting this version from SVN, then I am not going to recommend trying it for now.