Congratulations on getting a playable force finished. Only just got there myself so I know what a great feeling it is. Your Rhino interior looks fantastic, very subtle and muted - just like the Raven Guard should be - but still clean and crisp. Grey was a bit of an unorthodox choice, one I haven't seen before, but it really works. Nice touch with the purity seals.
As for the painting on the door I would personally do it white arrow with black symbol. While I think the whole white doors would look sweet, it feels a little overt. Depends on how much you want your vehicle to stand out or blend in with your infantry.