I saw you're using a 30 gal tank...just out of curiosity is that a 30 gal breeder tank (36x18x12) or a regular 30 gallon? I use a 40 gal breeder with a screen top for one of my snakes and also live in very low humidity indoors, so I'll just tell you how I do it and what I've experienced with some of the things you said you're doing.

I use a UTH under about 1/3 of the floor area of the tank. This is plugged into a rheostat (dimmier switch) in order to control the temp. I put several layers of newspaper directly over the UTH for extra insurance against burning him. I use a brick of shredded coconut fiber with a layer of aspen on top as a substrate. 1 brick of this stuff holds about 4 quarts of water and is not sopping wet...the aspen is more attractive looking but its main purpose is to keep my snake off of the damp substrate so that belly rot won't occur. I also use a 100 watt red heat lamp plugged into a thermostat that I can adjust to maintain whatever temperature I want. Because any type of bulb you use for heating will completely dry out the air in the tank, I covered the entire screen top with duct tape, except for a circle just a little larger than the lamp hood. With this setup I am able to create any temperature gradient I want from 95 hot side/79 cool side to about 82 hot/72 cool. I am able to maintain 80% humidity for a whole week before it drops below 70%, and I can keep it above 50% for a month. An alternative, as you mentioned would be to create humid hides. This will work for you because really your bp will spend 95% of the time in its hide anyway so why even worry about trying to keep the entire enclosure humid, right? Sometimes I do this when my snakes shed, but be careful that your snake is not constantly lying on damp substrate because it can cause skin blisters on its belly.

Anyhoo....my advice is to ditch the astroturf or whatever that was, because although it is an okay substrate to use most of the time, if you're trying to raise humidity then it's not going to help you at all. I tried the saran wrap thing too and it didn't work very well and looked pretty bad, so I recommend you ditch that too and just use duct tape...it still doesn't look that great but it works as good as a lid on a rubbermaid.

I'm sure you already know what your temps/hum should be at but just in case you don't know:

87-90 hot side
72-80 cool side
Ball pythons do not require a drop in temperature at night time, but if you wish to cycle your animals for breeding purposes just don't let the temps drop below 70...EVER.

I keep my humidity at about 60% unless one of my snakes is shedding then I will raise it to about 80% and maybe add a humid hide.

Well, sorry I rambled on, but I'm bored.....hope this helps a lil!

Jeremy