Was looking for the vehicle rules, but all I could find was mounted combat stuff. Am I missing something, or do I need to import stuff from the other systems?

Only War's got the newer ones.

The rules can also be found in Rogue Trader, along with all the ship stuff.

Note that the newer rules in Only War don't currently cover anything that flies.

Thanks guys. In your opinion, which would be better: use RT rules or use OW rules + RT flier rules? I have the main books for all the systems so I can pull from either.

Go with the Only War rules and adapt the RT rules for flyers (aeronautica). As a side note, I would also hesitate to use RT's starship rules since they're rather poor IMO, but there isn't really any official alternative.

My group doesnt want to use starships anyway. They favor a ritual from disciples of the dark gods as thier primary transportation. The only thing they ever want to do with ships is explode them.

Whilst I am obviously bias towards it, I really would use the Only War vehicle rules. They're the most up-to-date, most extensive and detailed, and cover ground-based vehicles more comprehensively than the ones printed in Into the Storm and Rites of Battle. No aircraft, but for all your ground-based needs, OW is there for you.

BYE