That would be the simplest. You wouldn't get much airflow in any of those 3.5" bays.
One alternative I've used is to mount thin fans (usually 60mm cpu) at the front of the case, in front of the drives. Whether this can work depends on the case, but even a small increase in airflow makes a big difference in drive temps. What's nice about it is you can cool 3 drives with a single fan.
About the brackets, I usually attach them to the underside drive mounts. Sometimes to the case itself. Drive attachment is easier. Modifying the case means disassembly or being very careful about debris. That depends on if it's a make-it-work build or someone's pride and joy.
Dilbert, I feel a drive temp test coming up.
