For the humidity, is there a way you just mix some moss in with the aspen? Or even switch to cypress mulch? At least that will help a little bit... Not more than the 50% you need though.

Heat wise, I think insulating the tank is one of the best ways to go. And maybe even split the 40g into two 20g. It would be pretty easy to do if you could house whatever snake is in the 40g somewhere else for 24-48 hours. Just use silicone with a piece of whatever it is you want to separate the tank with. I'm not sure how good the pegboard is for insulating, packing foam would be a good idea too.