If you are spending that kind of time flying B29s over strats, you could fly more than 37k feet higher than the strat and the puffy ack won't affect you.
Of course, some loadouts won't allow you that.
100% Fuel, 2x Ammo, 40 500lbers. That's my general load out. I tend to fly at around 30-33k when I did this since 1) I'm in a single and 2) I'm by myself. 37k would take too long even for me and taking drones won't allow for rearm. Not once have I successfully completed a "day tour". Once because I d/c'd, and this was before we had the d/c pilot thingy we have now, the rest I've been shot down by flak over the mega strat (again, last time I did a day tour). I later learned from Lusche that burning the central tank helps out a lot with fire from flak, but I haven't done another day tour to put this in practice.
Day Tour is what I call it when I log in and choose a bomber to fly with a single; for x amount of time (usually 12 hours), I sustain enough damage to end sortie, or I am shot down.