Fedora handles this with "tmpwatch" and a too large default you can create your own file with oerrides
tmpwatch and crones also wrong way.
says who?
I am. In Ubuntu, Gentoo, Suse and others no crons, tmpwatch, tmpfs and other bycicles. All clean.
no reason to remove ALL from /tmp while shutdown why do you bother about?
because cleaning /tmp is a normal system function
what is your PROBLEM?
my problem is a garbage in /tmp after reboot