if you were to stick with the foam, i would suggest leaving one BARELY filled with distilled water. that way, if you happen to screw up with the other three, you can kind of balance it out. after a couple of days, see what the average humil is, and it shoudl be lower than 70 percent. if that is the case, then add some pg and water to the barely filled one.
but not that much. just a little.
this will make sure you don't over do it, like i almost did.