I guess my question is "To what end?".
Good quality stretchers are made from No.1 Basswood which is relatively low in lignin and tannins. Painting them really doesn't seal them if your concern is acid migration. As Greg mentioned, only a metal (or glass) barrier will stop that. Besides, very little acidic gas escapes from the side grain of the wood, it comes primarily from end grain. Normal framing of canvases doesn't trap the gasses, and they are dissipauted before they can do damage. Sealed frame technology works by limiting the amount of oxygen available for oxidation but also has a whole new set of maintenance issues with it. Even with the metalized tape, you are still punching holes in it, effectively breaking the seal, with staples or tacks.
From what I've seen, the primary damage to canvases, other than impact, is weakening of the unprimed linen that is wrapped around the stretchers. Linen has wood protein, Lignin, in it and in the presense of oxygen will slowly self destruct. This area on a stretched canvas in a frame is also an attractive place for bugs and their debris which can accelorate the decay. Painting the stretchers will have no effect on that.
If you have a very valuable canvas to stetch, look at Trimar stretchers.
https://trimarstretcher.com/ for some interesting modern technology, or to Simone Liu for more traditional styles
https://simonliuinc.com/stretchers/