If you use RC paper, you will not be able to wax it due to resin coating. FB would probably work better for waxing. Try exposing through RC paper. The exposure will be pretty long, I image. I would take a metre reading on my exposure table through whatever negative you use and then another reading through a sheet of RC paper. Apply the exposure difference as a factor to your usual carbon printing time. Just be careful making your readings. You don't want to be looking directly at the UV light. If you have an incident metre, use that.