My greenhouse plants are doing very well just 2 weeks after transplanting to the grow buckets. I added black plastic covers to reduce evaporation and put in the tomato cages for support.
My grow bucket system seems to be working much better this year with very little leaking. I believe it all has to do with adjusting the float valve so the buckets don't overfill. I tried to set the float well below the maximum fill level because the greenhouse floor is not level. I still had to raise 2 buckets on wood spacers to prevent overflow. The upper overflow drain tube was probably not necessary once I got the float adjusted - but it is a backup in case the float valve sticks open. If I could re-design my greenhouse for Alaska, I would still want to insulate the floor - but I think a better option would be to use 3" rigid closed cell blue foam board panels placed below grade and covered with 3/8" crushed stone and maybe topped with wide spaced patio pavers. Then a little water spillage would not be such a concern. A raised insulated wood frame floor was a less expensive alternative - but water damage must be avoided. My greenhouse floor will never remain level due to winter frost heave.