you need a thermostat for your UTH or else your gonna cook your snake... Im gonna sound like a broken record but think about canning the 20L and get a 66qt snap top rubbermaid tub. Theyre clear just like a tank and a 66qt is pretty much the same size as a 20L. This alone should solve your humidity problem as plastic is a much better at holding in humidity than glass. Check out my gallery to see how I have my tubs set up... all 11 are pretty much the same and I have no problems. If you want some more details on setting up a tub shoot me a PM... Id try to help you with getting up the humidity in glass but I couldnt make it happen....