...is it possible to place multiple pop-under adverts on the same website?
Possible? Yes. But Highly not recommended, especially if on the same page.
I am currently using Popcash for a single pop-under which works fine and pays a small amount per day.
If the quality of ads are poor and/or your visitors have no interest in them, then you can expect low money.
...but i wanted to multiply that by maybe 2-3 pop-unders to launch on the page.
Now you're asking for visitor's computers to work twice as hard now. I feel sorry for any computer that has to go through what this computer went through:
I know they are not very visitor friendly but it is mostly one time visitors and I want to monetize the traffic.
Its worse than unfriendly. The more pop-unders or even pop-ups you have for a site, the worse it gets because they have to be closed down. (which is an extra unfriendly step on the user's end)
Has anyone else tried this?
I'm sure too many people have. If you want advertising, try to make it the least intrusive. That means a small ad in the page that can be scrolled away from view.