I think you already know the best answer to this problem - and that's replacing the aquarium with a proper-sized enclosure for your retic. But, until then....... Dry, patchy, hard-to-shed skin on a snake is a sure indicator that the enclosure it is being kept in, is too dry. Open-topped, screened over aquarium enclosures are notorious for causing this problem. In the winter, the humidity will become dryer because of the heating system for your house. The aquarium enclosure with it's open design and additional, electric heating installed, will become even dryer inside. This could be Bad News for the snake...... How to correct this problem?
1) I have seen interesting, do-it-yourself designs out there to modify the screen tops on aquariums to seal better and retain humidity inside the tank. The aquarium will also seal in the heat better if modified this way - watch out, and be ready to reduce electric heat settings! Placing a large, shallow water basin in the aquarium will release a good bit of humidity into the entire enclosure that way.
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2) Stir in water to approved, vegetal substrate mixtures like coconut bark, aspen, sphagnum moss, etc. Doing this will make the substrate itself nice and moist (NOT sopping wet!). Then, after moistening the substrate, placing a larger hide in the aquarium with a very small opening, and an open bottom, will retain almost all of the humidity inside the hide box/enclosure, where your snake will be spending a lot of time anyway.
