Ramp Room
I like shoving it half way down the main ramp, it really gets the poor bastards. Also good is on the edge by the touchdown zone - less visible to people coming from the second lower entrance and can also get RJers. Dispenser a bit down the spiral.
Ledge near Ramp Room Entrance
Either out on the really thin bit or next to the lift, they'll go thundering past to get to the ramp room and get shot in the back. Bwah ha ha. Dispenser just outside door - then the RJers will attack the gun and run through, the doors open and BOOM.
Upper Basement
You know, the place where the spotlight is if you det the wall. This is a good choke point as they can come down the spiral or along from the new back entrance. Either against the diagonal wall to focus on both entrances, or opposite so they get it in the face when they enter the room. Dispenser half way down one of the entrances to the basement.
Basement
One good idea is to place the Sentry gun in the darkness opposite the stairs along from the respawn room, with the dispenser just down the ramp to the flag. The second is sentry just down the ramp from the flag and dispenser somewhere outside.
