I’ve had lots of experience with 3M DP270 potting compound for sealing up cable assemblies and potting electronics. You want to avoid it coming into contact with certain kinds of non-fire retardant rubber or certain types of silicone though… which will prevent it from curing fully.
You can get away without using a static mixer tube and the ratcheting handle assembly, but those two make life super easy. So if you are going to be doing a lot of this, pick those up as well.
Make sure all of your connections are soldered before potting. Don’t try to pot over any type of connector, it will work its way in between your connection points.
You can speed up the cure time by elevating the temperature of the environment, which helps if you have a lot of these to do. Check the datasheet for appropriate temps.
Alternatives for an outdoor Core project might be a NEMA 4x water tight enclosure.