I try to dry down to about 70%, then begin curing with frequent burping to get to 62/65%. I have gone below 62% when drying. I don't recall how low. But, it's not an exact process. The outsides of the buds can contain moisture equivalent to 40%, while the centers remain 80%. So, I think they can go too far and be rehydrated within a short period of time (a day or two?). They're still living things, and that's part of the curing: to allow a certain kind of "death" (I guess it might be called, as the chemicals change, reactions occur).
You said you were waiting for Boveda packs. But, you do the wet sponge in a baggie. And/or exhale in the bag (if it's a relatively small amount). The sponge might cause the RH to go to 80%, but that doesn't mean the mateial has absorbed that much. So, you have to remove it occasionally to see where the buds are by themselves. (That's a good time to exhale into the bag, to replenish the humidity lost when you opened it.).
I don't know what kind of bags you're using. Plastic bags are not airtight. If you're in the phase where you're trying to hold the humidity (it sounds as if you are), I would use 2-quart mason jars. (Be sure to wash them before using. I think they're washed at the factory but the water might not be clean. They always smell funny to me when new.). Mason (or Ball) makes a 1gal jar. But, it's not a real canning jar. It's more for decoration. I've seen them at Target & Walmart. I use those for initial curing (when I'm trying to get it to 62/65 relatively quickly). Fewer jars to work with. The non-airtight lid helps. If I want to slow it down, I can put plastic wrap over the top so the lid seals better.