Oklahoma joe highlander temps mods

Ok guys a little help here would be great. I purchased a wal mart Oklahoma joe highlander.I have sealed all leaks by welding the fire box to the cooking chambers. Welded the gap around the fire box where the two pcs get bolted together and welded plate steel around the door to seal unwanted air from getting in the fire box. Welded the exhaust to the cooking chamber made a thin 22ga heat baffle. Put lava lock gasket around the cooking chamber added latches to the door a made a basket for charcoal. Did a dry run today with just some kings ford charcoal the temps across the chamber was about 30 degree higher on the firebox side also the highest temp was only 290 degrees I know that is pretty high for smoking but thought it would be much higher wide open even with the firebox door open. Do you guys think 22ga is to thing causing uneven temps? would using a pan of water on the fire box side of the cooking chamber help even out temps ? Also would putting a 90 elbow on the exhaust to the cooking grate help ? And with only getting 290 wide open today when outside temp being 86 how well will this be during the winter will I be struggling to keep temps in the 225-250 range? [/IMG]