jistjul Should I leave the domes on or off
You don't need domes over the mother tubers when they are potted up. Until they have sprouts, make sure the crown is slightly (1/4") covered with the potting mix. This will keep the crowns from drying out so no additional humidity is needed.
When you take the cuttings, the humidity around the cuttings will (probably, with your 20% RH) need to be raised for a few weeks until roots have formed. Most growers do this with a baggie or plastic container with the potted cutting inside. Commercial growers who take cuttings (indoors, with your environmental conditions) will sometime use a humidifier to raise the humidity of the entire room. This eliminates the need for plastic domes or baggies.
Probably the most important thing to remember is to not let the temperature get too high if you are growing under high humidity conditions. Too wet + too hot is bad for both tubers and cuttings. Occasionally, I still get careless and lose cuttings by keeping the rooting medium too warm.
