I don't know of anyone trying it with Seagulls, but when we deployed in locations that have both birds the crows interacted with the box far more often. Most of the work on cognition that I've read has identified Corvids as being able to demonstrate more flexible general intelligence, but you may as well try! I would think the biggest concern would be the gulls chasing off the crows and/or immediately clearing out the box in stage 1.
Let us know if you give it a shot!
- J