For me, avoiding rancidity means doing a bunch of things -- use quality ingredients as much as I can manage, work clean, store my ingredients properly, minimize metallic contamination, keep my hands clean when working with the soap, keep the soap clean and dust free in storage, avoid exposure to light, etc. And I'm looking into the use of chelators (EDTA, citrate) and antioxidants (rosemary oleoresin, ROE) in my soap as further insurance against DOS.
I try to do all of those things as well! It's tricky to keep them dust-free while they're on the curing rack, but I'm working on making a breathable tent for that. They don't get much direct exposure to light -- maybe 30 minutes per day on the top rack at certain times of the year, when the sun comes through one particular window at a specific angle -- but it couldn't hurt to have the tent shading them from that as well.
What portion of the curing time do you keep yours sitting out? I usually have mine on the rack for 4-6 weeks before I wrap them in paper. Initially I was putting the wrapped soaps in shoeboxes, but that's gotten cumbersome, so lately I've been stacking them in paper lunch sacks. They aren't getting as much air circulation as they do on the rack, but I figure it might be a little bit better than the shoeboxes. I often leave the paper bags standing open at the top.
I've been using sodium citrate almost since the beginning. I understand that Dunn's tests showed it didn't do much on its own to prevent DOS, but I thought it might help the soap lather better for people with hard water. I've recently been experimenting with using BHT as well. It doesn't seem to be a very popular additive, but the stabilizing properties of combined sodium citrate and BHT are highly appealing. Once I give a bar away, I have no control over how it's handled or stored, and I want to maximize the chances that people will have good experiences with the soap even if they store it in poor conditions.
So far I've done 3 batches and 6 small testers with BHT. Of those, one batch and two testers have turned bright yellow; the jury's still out the third batch. I made it just yesterday, so there's a chance it will also turn neon yellow in the next few weeks. Right now the theory is that it has something to do with fragrance oil, since a single batch split 4 ways and scented with 4 different FOs has yielded different results -- 3 portions turned yellow, 1 portion did not.
I'm planning on starting a new thread about the BHT discoloration issue, but since hardly anybody seems to be using it, I don't know if I'll get much of a response. My search of past threads didn't turn up very much information, and neither did a google search. What little I've been able to find on the topic is highly technical material that's way over my head.
If you have any insights, I'd really appreciate hearing them!