I'm not anal enough to put a humidity meter on it. The media will turn colors as appropriate. When I ran it open loop, I could see color changing fairly quickly. When I ran it closed loop, it didn't. I'm just trying to keep it all simple, yet effective. I've got 2 systems on 2 planes with 2 jugs of media in each dry case, and the media does a good enough job telling you by color change what the approximate level is likely to be. As far as I'm concerned, if it's pumping air through the media, which it is, it's definitely going to be good enough for me. My cases are sealed air tight enough that you have to fight a suction to open them, so there aren't many places for leaks. I also cap my exhaust pipes, so there's really very limited places for anything to enter the engine. Really just the intake is about it, and even that I plug on one of the airplanes with a cowl plug. I also don't worry about turning off the pumps. They run 24x7x365. It's just an aquarium pump, so not enough to concern me about electric cost. I didn't wait for the media to turn very pink before I changed it. Mine stayed very dark blue all winter, and when I first could see that the outermost layer in the jug was turning pinkish, I decided to regenerate it.
I do find that if I don't pull the dipstick and let the engine release its vapors, the media where the air comes in does turn discolored. So when I changed media, I sucked off the top inch with a vacuum cleaner and threw it away. When I did the regen, I did it for a full 3 hours. I watched a youtube video where a guy tested various time lengths and he saw more and more moisture lost measured by weight, based on time. It does decrease after 3 hours so I left it at that. It turned a dark blue and stayed that way after 3 hours. I also did it at 260 degrees, and did it in a few shallow pans where the media was no more than 1" deep, stirring every 15 minutes or so. I originally tried a large bowl and found that the stuff on top would dry well but lower levels would not. At least not quickly. So keeping it shallow and stirring fixed that.
For desiccant, I bought 5 x 8lb jugs of it. It takes just over 1 jug to fill my two half-gallon jugs for one plane. So basically I have a little less than 6 gallons or so ready in jugs when I need to change it out. I could get by with less, but I figure I'll regenerate them for both planes at the same time so that I can just take over the kitchen a couple times a year for one evening.
I'm definitely feeling very good about how this is going to work for the engines. It helps me worry less about if I'm going to be able to fly often or not. Right now, the answer is not...as I'm furloughed thru at least the middle of August. So with no paycheck its a perfect time to have some good engine preservation if I can only get out every month or so maybe a couple times.
Regarding the capping of the exhaust, I got vinyl caps on Amazon. Also got "remove before flight" keychains. Then put a small hole I the cap and tied the keychain through with rope and ran one end of the rope into the cap through a tight hole, thru a washer, and then tied it in a knot. Then siliconed the washer and rope right to the cap. So it's sealed up, and the remove before flight keeps me noticing the caps. Plus, my air hose going into the breather tube runs right between the exhaust.
This is one of those things that I think many builders should do for their planes. It can only help their investment stay rust free.
Here's a pic of the media color when I changed it. This is about 5.5 months with routine flying most of the winter. You can see the top where the oil vapor discolored some of it. That was my fault. A few times I went flying and immediately put the suction on. I should have let the engine vent a couple minutes first.