You asked for shotgun stuff, I will deliver.
I like to show off my shells, so I tend to avoid any type of pouch that holds them internally. Also, always make sure to not leave shells in elastic loops for any extended period of time. It will wear out the elasticity and make it where the shells fall out.
Here are my main shotgun specific pieces of gear:
Maxpedition horizontal shotgun loop panel. MOLLE with tac-ties.
Velcro backed loop panels.
21rnd bandoleer.
Condor MOLLE shotgun scabbard. Custom shortened to minimum length needed for a sawed-off.
And here's just a couple of loadouts featuring my shotgun that I have pics of.
For this one, I used black zip ties to rig the bandoleer around the bottom of my vest. Works great, keeps a low profile, and looks cool!
Something I threw on for a photo op.
This is the favorite shotgun loadout I have a pic of.