What do Mark and Alec do in preparation for their rescue mission in Chapter 48?

Alec explains that while Mark was sleeping he has taken the Berg up for a scouting run, and discovered that the people who took Trina, Lana, and Deedee are at the bonfire. They break into the central storage facility of the Berg, where they find a metal container containing guns. Alec explains they are Transvices: they make people disappear into thin air.