It can be done. I have a couple of things against slides myself.
1. Unless they are hard sided, they lose the biggest advantage of a teardrop over a pop up...noise reduction. I get very tired of listening to the entire campground all night, especially on the weekends.
2. Weight- if the pop out is hard sided, you add almost as much weight building the double wall and slide mechanism as you would just enlarging the trailer. Really, there's no gain.
3. Complexity- Sealing a hard sided slide against water intrusion on the highway is a pain in the rear. Not saying it can't be done, but again, it's much easier and just about as cost effective to add more space.
Having said all that, here's good thread on possibilities for a slide out bunk. Good luck and let us see what you decide to do!
viewtopic.php?f=2&t=26161