a tub\bowl of water won't help much. Put it over the UTH or under the heat lamp and that will help a little...

Try making some kind of humidity box.

I use a mesh pencil holder and stuff it full of aspen or moss. Soak that in warm water for several minute, drain, and put in the tank. Lasts at least a week for me and keeps humidity around 60%. I just cover more of my screen and get 80% during shed. You can also try a plastic tub\bowl with lid. Like a butter\margerine tub. Stuff it full of aspen or moss. Poke holes ALL OVER, and soak it in warm water in the sink for a few minutes. Drain, and put in tank.

UTH will work better than the lamps for keeping humidity right. But if your setup does not allow for that, you gotta do what you gotta do...