Marimba player looking to join a college drumline, tips?

I'm a sophomore center marimba currently at my high school. I excel at marimba but marching snare has been more of an iffy factor for me. I feel I've improved vastly recently and want to keep working to join my future college's drumline.

What would you guys suggest be the most crucial part in my practice? Learning to march? Specific warmups to play all the time? etc. I would prefer not to have a private lesson teacher over the summer due to money constraints in my house unless absolutely necessary.

(Sorry for my words being so long)