In reading about the SIPs online, I found a simple version you can make from plastic soda bottles.  Tried with some Autumn Sage (salvia greggii) cuttings.  Planted two cuttings 5/21.  Used RootTone on them.  Stuck into Hi-Yield potting mix.  Did not sterilize anything and used regular tap water (not distilled water).

Noticed mold/fungus growing on the mix in one of the containers after a few days, so removed the upper bottle cover for a while.  That resulted in some noticeable wilting.  I replaced the bottle cover but without the screw on bottle top, and that seems to have struck a good balance–plants are not wilty, no mold forming.

Update 6/11: one of the cuttings appears to not be taking–leaves falling off, and a slight tug on it did not offer any resistance, indicating no roots forming.  The other cutting seems to be taking–leaves fairly healthy looking, it does not wilt when I remove the cover, and a slight tug offered resistance.  So there is hope!  I guess I need to wean it off the humid closed planter bottle and maybe feed a bit to get it growing on its own.

Overall, I did practically nothing to care for the cuttings.  I left the cover on (without the screw on bottle top) pretty much the whole time.  I did not mist or add water–the reservoir stayed plenty full and the potting mix stayed moist.  Going to try a few more cuttings of different plants soon.