I don't have a heated garage so I use a heated 5-gallon horse bucket, they also make a 16-gallon if you plan on to keep a lot of bait.
use a plexiglass cover if you get jumpers.
I use a hang on carbon power filter and an air pump with an air stone.
Set the filter flow rate on its lowest setting so the minnows don't swim themselves to death
Make sure to do at least a 50% water change once a week, I usually do a full water change.
Which is easy since its only 5-gallons, I keep saying I'm going to bump up to the 16-gallon, but haven't yet
I use an Ink-Bird temperature controller to better control and fine-tune the built-in heater in the bucket.
I set the temperature so the heater turns on at 33 degrees and turns off at 37 degrees. The residual heat will bring it a bit above 37 degrees.
I put the controller's temperature probe in the filter box to help keep it out of the way, but directly in the bucket would be fine too.
The heated bucket by itself with no controller gets too warm and get too warm too quickly, which freaks out the minnows and they don't last very long.
I have had great success with this setup for several years now.
The bucket plugs into the controller and the controller plugs into the wall outlet
Make sure to use the heating side.
Good Luck All