Try little things of water. Like a custard cup etc...until you find the right surface area to get the correct humidity. If the glass isn't holding temp you may want to put some styrofoam around it. May insulate it enough.
I have a thermal blanket wrapped around three sides and the bottom. The temp has been ok. The humidity seems low but I think I could modify the cover during lockdown if I decide to try to hatch in it. It would be fun to watch hatching through the big glass.
