I have also tried the same as author of this thread and succeeded (until one point )...
I have added 3 popunder codes as 3 "1x1 banner" .. Also, I have setup them to different GEO countries and that also works as a charm...
The problem:
Most of companies that pay for popunders usually shoot 1 popunder for 6-12 hours, so I have tried to give them "Delivery capping per visitor" option. To maximize revenue, it is important to me to try to serve as much popunders as I can.. My idea was to create some kind of "backup tag" with lower weight (and that also worked).
Well, in short lines, I have tried with "Limit banner views to" per session, but when I do that, the number of shown popunders drops for 5-6 times... It is interesting that it is totally irrelevant what number I put in that field (I have tried with 3 and 300)... It always shows the popunder X times (X - number 5-6 times lower than without capp)
Is there any solution to this? I know that "banner field" is not suppose to be used for popunders, but if it works, why not?