I was thinking that the Armscor VRBP-100 Rastus has would be a nice shotgun to have for a house gun since it's compact and seems to be well made. Then I found out about the IWI Tavor TS12 bullpup. Instead of a 5+1 capacity, it has a 15+1 capacity with an overall length of 28.34 inches. It only a 12+1 capacity if you're using 3" shells instead of 2 3/4" and there's a button to switch between them on the the gas system. You could also have 13+1 or 14+1 depending on what length shells you load into how many of the 3 tubes, but I would stick with 2 3/4". The 3-tube magazine isn't detachable, but if you need more than 16 rounds of 12 gauge you don't need another mag, you need a different gun IMO. Preferably something that starts with AR, AK, or M. And belt-fed would be a bonus.

When one magazine tube is in the feed position the other 2 can be loaded from both sides. My advice would be to make use of cover
always, and do tactical reloads keeping a full mag tube in play when you can.
The ultimate in shotgun firepower AFAIK is the SRM Arms SRM 1216 with a
detachable 4-tube magazine holding 16 rounds of either 2 3/4" or 3" shells. They make a version of it called the SRM 1228 that's designed to shoot Aguila mini-shells. Fire 28+1 rounds, pop in another 28 round mag and keep on going.

Can you imagine how long a 28-round box mag for a 12 gauge would be? That would be sure to get in the way and get damaged, but it would make for a handy monopod.

The SRM 1216 is built with an ambidextrous receiver so you can set it up for either right or left handed use. There's even a California compliant 1216 (each tube holds less than 10 rounds so it's legal) with a magazine lock. And they have 10" and 13" NFA models listed for law enforcement, with 8 round and 12 round mags respectively.
Neither the Tavor TS12 or the SRM 1216 is cheap, but the SRM is way more expensive than the Tavor. The SRM is priced beyond what I consider reasonable when I see some of them listed for sale around $1,200-$1,300 more than a Tavor elsewhere. I haven't seen both on the same site to get a better comparison, but it's not even close. It's almost double the price. The Tavor's a heavy gun but I wouldn't be carrying it on me. I'm still thinking about getting one when I get my ATV paid off. At the rate I'm going I'll have my loan paid off a year early. I'm trying not to buy any new guns until then, just accessories.
https://iwi.us/product/tavor-ts12/ https://www.srmarms.com/