I have a couple mods I did to mine and I get a solid 8 hrs from it on about 10# before it drops below 200 degrees
1> Damper on the bottom...I made a slide one and then the
2> fire grate in the fire pan with about 1.5" clearence from the bottom pan. Just some large bolts and double nuts
I do notice I can run it virtually shut down for the first couple hours and then I open about 1/4-1/2 way At about 6 hrs I open more air and keep the temps up to around 240-250. I also give it a little kick to clear any ashes not falling down.
Can't beat them for the price.
I was looking to change from water as well but have not tried sand or clay pot base yet.