I dont know if I mentioned that I kept and bred various reptiles for over 20 years as well, and this next idea stems from the units I used to keep some of my snakes in.

they are plastic drawers which I drilled holes in the front for ventilation. I also cut out the front and pop-rivited clear perspex on the front so you can see in.

I think these drawers will be great for raising multiple slings.

heating is supplied by heating cable taped to the roof of each level of cages as seen here. Temperature inside drawer gets to mid twenties C.

Small container with screw on lid for housing slings. Ventilation holes made with soldering iron.

These drawers can hold 140 of the smaller growing containers on one level

as the slings grow they can be rehoused in bigger growing containers (big enough for quite a large tarantula already).

these drawers hold about 70 of the bigger growing containers.