Line a 9x5-inch loaf pan with plastic wrap, letting the ends of the plastic wrap overhanf the pan by 6 inches. Scoop the ice cream into a large bowl, then work to soften, Fold the peanut butter into the ice cream until uniformly mixed.
Working quickly, arrange 8 chololate wafers to cover the bottom of the pan, (some overlapping is fine). Spread one third of the ice cream mixture evenly over the wafers and smooth the top. Spread 1/2 cup of the caramel sauce over the ice cream. Repeat this layering process two more times. Finish by laying the 8 remaining wafers over the top and press them lightly. Wrap the pan tightly with plastic wrap and freeze until firm, about 6 hours.
To serve, unwrap and gently ttug at the overhanging plastic wrap to remove the loaf from the pan. (If necessary, dip the bottom of the pan into hot water). using the plastic wrap to handle the loaf, invert it onto a serving platter. Peel away and discard the plastic wrap. Allow the cake to sit at room temperature for a few minutes before slicing.
TO MAKE AHEAD: this ice cream cake can be assembled and held in the freezer, wrapped tightly in plastic wrap, for up to 1 week.