You shouldn't have a problem with the humidity if you live in the uk. I have never had any problems with my snakes, past and present regarding bad sheds. If you are unsure test the humidity in your vivs and if it is low then use a shed box when they go into blue or mist the viv every now and then when they are shedding. Chances are though, you probably won't need to do anything to help when they are in the shedding process. The humidity in my viv is around 40-50% when i measure it every week or so. Which is fine for cornsnakes, i sometimes raise this when they are shedding.