If you added a baffle in there, even a partial one, it would help keep the fluid from sloshing around so much and turning into foam. You could put two in there, one in front and one in back with a gap between them to allow the wands to dip into the fluid. This will still allow easy refill of the fluid.
If you're using stock bubble fluid and the fan is still running a little to fast breaking some of the bubbles, you can add a spoonful or so of Dawn to each "tank full" to improve the bubbles survival rate. Just don't get too crazy with the Dawn, I already made that mistake in a Halloween cauldren on our front lawn. 1 bottle of Dawn equaled 1 big bubble mess on my front lawn............although the kids liked it!
