IIRC, either Burris or Leupold has a red dot mount for their optic. Installs between the butt stock and reciever.
I'm not up on all the current options. I've had a Armson OEG on my LH Remington 1100 slug barrel since the 80's, long before red dots became popular. It's DYI, engineered by me.
I took a set of 1" Millet vent rib shotgun rings and had them adapted to mount on the base of the factory mid barrel open rear sight. Friend was a machinist and he open them up and cut the correct angle in the rings to match the Remington base slope. Replaced the set screws with button heads and tapped the side of the soldered on factory base. No need to drill and tap the receiver. Don't need the red dot, just swap barrels. I used a Armson OEG but a Ultra-Dot could also be used.
Necessity is the mother of invention. This setup was used for years, in Michigan's
shotgun only zone, with great success. Since it's now used exclusively as a home defense/varment getter, I added the flashlight with forend switch and wiring.