I've heard of pulling some water in them when not using them, but i have 2 issues there.
1. The gaps are too big, it would be a long process
2. I wasn't paying attention on one of my test smokes and lit the bottom of the barrel on fire. It happens. I cut out a circle from some plywood and pounded it into place. That part is really not watertight.
I started reading the UDS subforum, I am pretty sure the gaps are causing the fluctuations. I also need to build a new ash pan and fire box from expanded metal. I thought of a high temp silicone, but I really didn't want that near my food. I think I am going to rip some slivers of something flexible, get them wet and cram them into the cracks and staple them in place. Who knows.
If that doesn't work I'll sell someone the kit- hinge, chain, exhaust (I think it came from a Chevrolet), firebox and grate and my wife can turn the barrel into a plant box on the porch.