I seem to be having a great deal of trouble figuring out how the "correct" canonical way to do things on the maemo platform are done.

I already mentioned adding to /etc/sudoers(.d)

I've also tried porting davfs2, but other than manually, how do I add the user and group for davfs? Or should these things be in install shell scripts and if so is there a standard utility or way of doing things?

I would assume you would handle it in a postinst script as part of your .deb file with tools like groupadd and usermod.