I have them in a rack system.
The new ones were QT as they had mites.
I have used Provent-a-mite everywhere just in case.
I was very careful when I used it.
No mites at all, now after 12 days.

warm side about 28,5 C.

air temp in the room about 21 C.

The rats are at the same spot years now.

I have noticed that sudden deaths were noticed when I bought some new rats to complete my sets.