I think the tube idea is ok but could be a lot better. One thing is the roots circle. I've been reading about root circling problems in small trees. They use air pots to stop this. Also corrugation in the pots to channel the roots. What's needed is a air pot like a tube. I've got some ideas. It would be made of silt fence(low cost). There has to be a way to reduce labor though. Maybe something like corrugated cardboard but made of silt fence. I'm thinking about it. Maybe a template could be made to fill the silt pots then reused to do another set.