Tinfoil
from what ive heard tinfoil works the best out of the options listed above. i use tubs and when trying to raise the humidity i use 'the sock trick'. take a clean sock, soak the end of it in warm water, fold the sock back into its self and place over the heat sorce. this last far longer than misting and does not spike the humidity out of nowhere but raises it slowly and keeps it up. with you set up i would try tinfoil over part of the cage.