I'm not real sure I can be any help to you as I have not used the beads in a true humidor. I have two Igloo Polar 120 Quart Igloodors and I have put a half pound of beads in each one. So far they are holding the RH exactly where I want it (65%). BTW I got the 65% versus the 70% variety because I've found a slightly drier cigar does not have nearly the draw problems that a higher RH can have, and it does not seem to detract from the flavor at all. For a true humidor, as a guesstimate, I would say perhaps 2-3 ounces. And remember it takes very little distilled water to refresh them. I don't believe I would leave the credo in the humidor along with the beads. To my way of thinking that would make it much more difficult to maintain the RH you are looking for. One problem presented by folks is what type of container when you are talking about using that small amount of beads. The best idea I have heard is to use the plastic 35mm film canisters and perforate the tops. They are easy to open and refresh with distilled water and they take up very little space in the humidor. You are probably going to have to experiment a little, i.e., the 300 count humidor may require two, one in the top and one in the bottom, the 100 count should get by on one.
I'm flying by the seat of my pants on some of this as I never tried it personally. Hope it helps some. Perhaps some other BOTL on this board can add to it. Good Luck!
PS: I will say that since I started using the beads, I'll never go back to foam. The beads are far superior in my opinion, in consistency and stability.