@Jim, you said: Once the fiberglass is in place the toilet can be hooked up to the venting, and a pipe installed to the urine collector that would lead to a drain pipe connected to the gray tank under the sink.
Am I understanding correctly that you're suggesting draining the urine collector into your gray tank along with other waste water created when washing dishes, showering, etc.? Shouldn't you then always dispose of your mixed "gray" water in a human waste repository? Otherwise, gray water can often be disposed of less formally, namely, on the ground in many places. I know gray water disposal varies considerably, but seems like this idea may limit your options. Somebody please correct me if I'm wrong here.