Bottle Spunding Trappist Ales

I’m not sure of the Oxygen permeability of buckets over the course of 3-4 days, but I’d wager the active yeast makes quick work of the minuscule amount introduced via that pathway.

In short, that should not be an issue with 3-4  days worth of vigorous primary fermentation.

Aha.  Not an issue, I don’t think, during fermentation.  The yeast are actively scrubbing the oxygen.  The concerns with the permeability of fermenters that I am familiar with are more along the lines of bulk aging or letting the beer sit for a length of time after fermentation (like a couple weeks or whatever, not specifically aging).

I am not a low-oxygen guru, however. Maybe stainless is more better?

I’d be all over a 2 gallon SS vessel. I’ve contemplated a 2 gallon kettle for some time, just haven’t made it a reality yet.

I haven’t had any issues with my buckets.

SS brew tech now makes a 3.5 gallon version of their stainless brew bucket, though maybe that’s more headspace than you would want.

A 1.75 or 2.5 gallon corny keg with a cut dip tube would be sweet but would require a lot of extra gear for someone without a kegging setup.

My buckets have been great so far. I have entertained converting a kettle as well.