Well Bruce, After waking up this morning, I realized that you really do not have many options available. A cone bottom tank may be your best choice, given the circumstances.
The short ones without the lid would be a better choice.
If you can, try rig up a delicate water jet system to keep the feed suspended. This would be an upflow device. Will it really make a difference with sunfish?
Cone bottom tanks were dismissed many years ago. The initial thought was the conical shape would be an aid in self cleaning. This was proven not to be the case in standard recycle systems. But for feed training in your situation, it makes sense.
I don't know anything about hatching sunfish, and never looked into it.
Would anyone know if it would be beneficial to keep them crowded? keep the tank covered? and with an internal submerged light? Any other beneficial insight?
The coolest feed training rig I saw was from a fish hatchery in Canada. Very successful, but very expensive.
I forgot that you are not going the full blown recycle rout, which makes it a different animal. Not as complicated. Maybe it's just me, but I would rather toss a few bucks at it, rather than a whole bunch of hours.
