Well,I am suprized no one has chimed in. White lipped tree vipers seem to tolerate a wide range of conditions and I would also include Borneo and flat nosed vipers among those relativly easy to keep. Eyelash viper would also fit in here too if they are established. As I hope you know, yearling snakes are less likely to get into trouble than newborns or hatchlings. Hydration is the ever important parameter but you can over due and keep them too damp and this is probably worse than too dry. Hope this helps, I am sure others will add their opinions.
Bob H