Is the environment in the band hall the exact same temperature and humidity and barometric pressure as inside your band hall?

If not, you need to tune outside. All three of those factors affect tuning.

Do all playing and tuning outside. I usually follow relative pitch and tune the band to where the tubas hit naturally outside. Now only if we could adjust the relative pitch of mallets.

There is a considerable environmental difference that will affect every instrument differently. You have to tune outdoors to perform outdoors. The trick here is to train your students to use tuners and buddy system it. Hold for the other, and then check the other. Unless you are lucky and have contest in 70-72 degree temps outside I would never leave it alone with just indoor tuning.

It’s part of why I do not like indoor warmups for marching band contests.

Tune outside and tune to 442.