Put two 1/4 thickness Solid Concrete Blocks in the gas oven and WOW! Much more even cooking.
This isn't FDA approved so proceed with caution if you try this but it worked for me! I was trying to find a way to give my cheap gas oven a little more even/radiant heating so I picked up a pair of 1/4 thickness (about 1.5" thick with the usual dimensions in other directions) concrete blocks from Walmart's garden dept. I popped these in the oven (wrapped in foil to protect the oven and the bricks) and fired it up... they are almost a perfect fit! So far I've had them in there for about a week or two and I like the results. It adds about 10-15 minutes to the preheat but it's a very even cooking now. I've made several bread loafs and a DiGorino pizza. Everything I've put in there has turned out great. The crust in the store bought pizza REALLY stood out. It was fluffy and soft and it was actually done very evenly. We all thought WOW! for the first time about a DiGorino pizza. Usually we make fun of their slogan (the whole delivery thing) when we eat one of those. This time it really was a great pizza. I was surprised.
While I was at it I also added a Steam "feature" and it's also worked great. I added a big canned tomatoes can (28 oz approx) with the label and glue removed (important) and with a tiny hole punched from a drywall screw head (Drill bit holes were too big I thought) and this filled 3/4 with water and place in at the end of the preheat gives a nice steamy oven for the first half of a bread (or pizza baking). It's really worked great! And it's adjustable by the size of the hole.