When the game starts me out on the Tower level, it only gives me about 1 min of filters and hardly any ammo. This isn't enough to complete the mission. Are there any filters to be found on this level?

Update: I think I figured it out. During the sequence when the buggy gets flipped over, a small ammo crate appears and it has some filters and ammo in it.

Probably too late now, but once you are up the tower there are once again more filters than you can reasonably use up!