I've had my homelab for a couple of months now and up until it has just been lying on the floor in my living room, which is kinda annoying. So I decided to mod the case a bit, so the whole thing fits my Kallax. :)

I'm still monitoring the temps but they seems fine when idling and under load. There's holes as the back of the shelf, but you can't really see them in the photos. I get around 35°C on the CPU, which is only 5°C higher than previously.

The hard drives are also fine temp-wise. I glued them to shock-absorbing foam using double-sided tape and left enough space for ventilation.