Remember this is a G rated family board, guys.
No more dissing of Vettes or gals named Tiffany.
As for the question at hand, Karma is Karma and chopping that BT99 will get you at least one incarnation as a trap boy at a club full of accident prone, no-tipping, idiots.
Maybe a couple.
If you want a woods runner single shot,get something like.....
An older H&R, NEF, Stevens, Winchester 37A(Sorry,the 37s are all gone to card shooters)or even a Brazilian job like Rossi in the gauge you want.
Fit a premium pad(Trust me) and if you insist, trim the barrel back to the legal minimum of 18".
Find appropriate ammo in 2 3/4",no Maggie Numbs, and have fun with a 4.5 to 5.5 lb tool that redefines the term "Hard Kicker".
As for finishes, Robar, etc, provide a variety of hard, rust resistance surface treatments that work well but will get you back much more than the nominal cost of the arm itself.
A couple things I've noted from seeing these projects for a very long time.....
A single shot with 28" barrel and standard stock is a skosh shorter than a riot barreled 870 also with a standard stock. That 870 is hardly long and ungainly.
The little NEF 12 gauge here has a 28" barrel,handles like Zorro's rapier and weighs 5 lbs, 9 oz. Carries like a walking stick.
It does kick very well, but the standard loads I use are 7/8 oz reloads and the back end has a KickEez attached.
A 20 gauge set up similarly would be slightly lighter and even more nimble.
And a wipedown with a rag and Mobil One keeps it the way it began.