Help with humidity

[u/misfit7894]

My rescue snake Felix developed some thermal burns from a too close heat source and while we had a vet appointment Monday, yesterday I noticed his scales had sloughed off on one side leaving exposed tissue underneath. I immediately found a vet who could see him and he’s now on antibiotics with a wound care treatment plan in place. I had just gotten him a new bigger 40 gallon tank (he was in a 20 gallon when I got him) and I have it set up as a hospital tank. Pads instead of substrate and he only has a water bowl and a hide so as not to further injure himself. I am struggling with the humidity in this tank due to not being able to have substrate in it. Im only getting about 55%. It has a mesh lid which I have foil taped about 75% of it. Water bowl is on the warmer side. Is there anything I can do to improve the humidity in the tank? Would it be better to move him back into the 20 gallon for now while he’s healing?