My spotted had a bad shed over the weekend, I didn't notice he was going into shed so didn't make him a humid hide like I normally do. Once I noticed I put some damp paper towel in his warm hide and the rest of the shed came off in a single piece.
I give my snakes large water bowls that they can soak in, and never had any shedding problems. I also live on the coast in north QLD, so humidity is probably not an issue here anyway.
While humidity can be an influencing factor the most common cause of bad sheds is a lack of hydration.
As we generally feed frozen thawed the food items tend to lose some of their moisture content and as such I have found the better solution is to feed them 'wet' food.