Having two hulls means that two masts don't necessarily have to go one in front of the other.
Junk sails are traditionall flat, taking some bend with the battens in a wind. Thus it makes sense to think of making a junk sail from a polyethylene tarpaulin or other plastic sheeting. Here's how
A modern-day designer of ocean-cruising junks offers a variety of designs suitable for the rig.
An active discussion list on the Chinese rig.
A yacht designer gives a good job of describing a junk rig's "impressive list of positive attributes." He talks about suitable hull forms, safety, sail stress, and other points. Kasten has designed some of the most attractive junk-rigged hulls around today.