TCW - Express Sight Systems make a Tritium setup for shotgun rifle sights (to replace the Remington sights on their slug barrels, for example). For those liking bead sights, but wanting something for low- or no-light use, they also offer three styles of tritium beads that can be epoxied over the existing bead, giving night aiming capability. See http://www.expresssights.com/.
For HD a bead will do fine, but a GR on your shotgun will expand its capability. Slugs and GR sights make a great team when it comes to hitting a target out to 100 yrds. Which you may very well need to do someday. Get the GR sights. Dont limit yourself.