buying cyrpess mulch from a pet store is quite expensive. buying cypress mulch from home depot and lowes is INCREDIBLY cheap. for a large 15 - 20lb bag was below 4 dollars. the cypress mulch really helped my wife and i control the humidity since it retains moisture well but doesnt mold. (a herp guy told me to do this)

also, i had a screen top too. i would put a towel over it so my heat wasnt escaping along with all my humidity. i have heard of people putting saran wrap on parts of their screen.

one more tip that helped me which i read on here was: put your water bowl above the area your under the tank heater was to produce more evaporation which in turn causes more humidity. i put half of my large water bowl over the UTH and it worked wonderfully.

one last thing. i noticed you might be using the classic humidity/temp gauges. i noticed my humidity seemed more accurate once i went to wal-mart and spent 11 dollars on a Digital combo temperature (indoor - outdoor with probe) / humidity gauge. my old classic dial humidity gauge measured the humidity at that precise spot. i could move it across the tank and get a completely different reading.