I have made several mods to mine, I used 1/4" steel plate to make a baffle to force the heat below the bottom rails, then I bought 1/4' x 2 x 14.5", 16 of them to go across the rails all the way to the end of the chamber. I am still tuning the bars trying to get the spacing right. I also added a plate of sheet metal on the exhaust end that fits the inside diameter and goes down to the grate. I'm having a great time with it now, temp spikes are not a big issue and on long smokes the temp uniformity just keeps getting better as the heat warms the steel bars up, I use a water pan directly on top the baffle.
I have thought of getting some thick perforated metal with like 1/4" holes to put under the bars to help transfer the heat to all the bars a little faster but haven't done it yet. At the moment I use an IGRILL2 one probe in front one in front of what I'm smoking and one at the end and the other 2 I put in what I'm smoking, when needed I have a REDI CHECK to monitor the heat and track the meat with the IGRILL.
I also sealed the lid with high temp silicon and added a piece of expanded metal to the grate in the fire box.