That is weird about the humidity going down in your LG when you put the red plug in mine goes up wheni do....
I keep humidity in by opening the red plug (to lower temp and or humidity) andi keep it stable by either keeping teh plug in if it's too cool in the room, ori take it out and cover the hole with a peice of paper towel if it's a stable nice temp in my room an that holds the temp steady....
I also have tape around the whole edge of my incubators top lid so that it takes the humidity and heat jsut that little second longer to seep out...i also have a towel wrapped up around the one side of the bator and it realy seems to make a huge difference...
wheni need more humidity i get soem really hot water, i have two cups in the bator, one with a folded up paper towel standing up in it...i sprinkle water directly on that towel and the excess water flows into the cup....the other cup i just pour water into as it's a shallow container...then i pour more water into the basins inthe bottom, and i haev about 3 folded paper towels in there that are just laying in there that i dampen with the hot water...
five mins later, ive got 68-70 humidity adn it'll stay taht way for days unless i open the bator up.
My temps actually fluctuate more than my humidity does but through trial and error i keep it easily around 99.5-102.