Tank humidity question

I am posting this here since I can't get any answers about any other species of reptiles anywhere else on this forum. I see most of the people here (including myself) have other types of reptiles, so I figured I might have a better chance of getting an answer here. I have a "leopard gecko" that requires 50%-60% humidity. i have my "gecko" in a 40 gallon breeder tank with 12 inches of 60%-40% mix of soil and sand. I have a wooden lid with a mesh screen only where the lights are. The "gecko" requires a basking spot around 120 degrees. I have a UVB/ 50w halogen heat lamp combo and a 100 watt heat bulb. With this set-up I am having problems keeping the humidity constant. I am spraying the tank a couple of times a day with a half gallon of water. The humidity will spike to 90-100% but then by the time I get home from work (10 hours later), it's down to 30-40%. I don't want to get an automatic mister because the UVB/halogen lamp has warnings telling me not to use it in a moist environment (I move it when spraying water into the tank). I was thinking about adding some coconut husk to the media since it holds water better. Would a UTH help by maybe evaporating some of the moisture that is soaking into the bottom of the tank?

I admit to having other reptiles and being guilty of hanging out mostly on the leopard gecko board. =P

It would probably help to know what species you are dealing with.

I live in New Mexico and it is very dry here. The only way I have found to successfully keep anything that requires elevated humidity is to partially seal the tank. However, with a basking temp at 120, I don't know if my method would be safe. All of the herps I keep that require humidity don't need temps anywhere near that. For example, my treefrog requires humidity around 60% but temperatures only in the mid 70s to low 80s. To accomplish this, I have plastic wrap (I know, real high tech. It works, though) covering 3/4 of the tank, I mist twice daily, and I stuck a UTH to the side of the tank (regulated). This keeps the humidity and temperature just where it needs to be.

I did read somewhere that you can use a wet towel to partially cover the lid.

With a 50 watt bulb and a 100 watt bulb, I might be reluctant to also add a UTH. It might get really warm in there. You also shouldn't put a UTH on the bottom of a tank with a thick layer of substrate.

Coconut fiber is definitely my friend here in the desert. But that also depends on what species you are keeping.

All of this would still depend on what the species is and if it requires good ventilation.

Baby savannah monitor. I am expecting him to last 6-8 months in this cage while I design and build a really big enclosure for him.

I don't know much about that particular species. But this page: Correct Savannah Monitor Care talks about creating humid burrows, I am guessing a lot like humid hides for leopard geckos. What if you tried that?

It also mentions a humidity gradient (60% on the cool end, very low under the basking lights, and nearly 100% in a burrow). I wonder if you couldn't cover about 1/2 of the tank with something on the side with no lights (wet towel, a piece of plexiglass) and then also create a super humid burrow. Perhaps you could dig one and support it with a structure (excavator clay?) on the sides of top. If it's deep enough to where the substrate is really thin, you could run a UTH on a lamp dimmer (I imagine you would want to run it on very low so the burrow doesn't get too warm) right underneath it to help create a very humid burrow. I suppose a regular humid hide would accomplish the same thing (wouldn't be as cool, though! =P)

But again, I don't know a whole lot about that species. I'm just throwing ideas around. I just wanted to give my input because I often have the same struggle with other species.

If you look in "other lizards" under savannah monitor set up you can see pictures of the cage. Underneath of the basking spot brick I have 2 heavy pavers to keep it from sinking and I dug a cave in between them. Instead of spraying that area, I pour water over the basking spot so it will sink down and keep the cave moist. I could try to seal the lid better. It is mostly wood but it could leak some humidity. I do have a cork cave on the cool side that I spray excessively. My only humidity gauge is hanging on the rear center of the tank so I am only getting an overall reading for the tank.