I wouldn't worry about the O2 ingress. As long as you've got fairly active yeast going in there, it will mop up what little you let in before it can do any damage - at least as long as you take care to not bee too careless.
I've got a lot of faith in yeast
. I've been dry hopping my NEIPAs for a long time with no extreme measures, and they've shoved no signs of oxidation. And I'm bottling all my beers, too. And oxidation really is no issue. (This of course is anecdotal evidence, and thus is no evidence at all
. It's just a data point. But it's a fact my NEIPAs are not oxidised.)
For some science to back this up, you can go to George Fix'
Principles of Brewing Science, p. 130. He states that oxygen absorbed at room temperatures will remain an inert gas for a long time, giving the yeast plenty of room to handle it.