Vivarium size is a minimum of of 92cm (length) by 45cm (width) by 45cm (Height). Not sure what 30 gallons is, so i don't know if that is adequate size. The vivarium should be made out of wood, with a glass sliding door at the front. You should be able to make a viv of this size for a lot less than buying one already made.
Five lined skinks like to live onany moisture retentive substrate (orchid bark is a good chice) with a covering of sphagnum moss.
A lot of people claim that skinks get on well without UV light, but it is highly recommended that you get it.
72F at cool end, 88F at hot spot, and reduce to 65F at night. They have a photoperiod of 12 hours.
They like a humidity of around 55-60% so a light spary daily (on the moss) will keep the humidity.
In winter reduce the temp to 55F for 8 weeks, with a photoperiod of only 6 hours
Five Lined skinks eat any dusted invertebrates (locusts, crickets, mealworms plus stuff from your garden) Feed them a varied diet of fruit and veg aswell. If you want, they can be given a pinkie once every two weeks, and it is advised to provide small pieces of cuttlefish bone for extra calcium.
Any more questions, please ask