You use a heated water bath or tray to keep your bottles of chemistry at the correct temperature.
And you want enough solution volume in the drum so the temp doesn't drop during development.
A prerinse with correct temp water prior to actual dev will help condition the inside of the drum. I
use RA4 chem at 84F. But ambient temp in the room itself shouldn't be so far out of whack that
you get a temp drop in the general process (and I live in the Bay area, so know what 50 deg is like
even midsummer!). Drum work way better than trays anyway, and are safer on your lungs. Make
sure you have decent ventilation!