i have a T3 and the warm side is just fine but i was wondering

1.If i put a sheet of metal ontop of the Heating Coil (in the tank under the carpet) would that spread the heat better? or would it just mess up the temps?

2. on the cold side i have a heat lamp and its KILLING the humidity. Can i use a regular UTH (the zoomed reptitherm thingys) instead? or would they melt the bottom of the T3? also i have it in two sizes the 10 gallon and the 40 gallon? (its longer) which should i use?