Probably it is looking for the "dist" file of your module *outside* your module directory (re: Trying /home/peter/prj-src/perl/Saltydog-BlogBackup/>>>>>..<<<<<</Saltydog-BlogBackup.tar.gz)? cpanm can not even find dh-make-perl and some of its dependencies to install on my linux box (and that does not bother me much) so I can only guess from that missing tar error message you posted.

Update: as syphilis also mentioned earlier, sorry for the duplicate.