Seedling/Rockwool Fail, WTF?

I recently had a couple seedlings shirvel up and die after only about 4 days using the plastic bag method.. After sprouting the seeds using the Paper towel germination method. Whats the best location to store the seedlings/Rockwool cube to root before placing the cubes into my hydro system? Would a simple Grow tray/dome work?

i use rockwool cubes in a dome same as i would my clones

i use a lil heat pad underneath my cubes aswell to help support root groth

yes it would, one with breathe holes. u basically suffocated them by denying them oxygen is sounds like.

Ok thankz, how long does it take to see roots, after placing the cubes into the dome?

sry edit, forgot we were talking about seeds not clones...generally 3-5 days.

You says your seeds sprouted right? As in there were leaves?
Once the plant shows first signs of leafs then you have to take it out of the humidity dome or whatever your using to humidify them. After they break the top of the medium, put them in open air and sunlight, or whatever light you use. You probably suffocated them.