I dont think there is a way to set an element height to be 100% of the viewport with the new responsive engine. 100% of parent height has become quite easy (It was really troublesome before the new responsive engine).
One way to do this is to apply css to the element using the Classify plugin.
The matter has been discussed quite extensively through the forum, here is one post that discuss it : Setting a group to be % of viewport height dynamically - #91 by d9999