Gene, as I mentioned, I use GPS coordinates only to locate the approximate timing points, not the course route. I record the path using tape measurements from fixed objects. I add compass directions for clarity.
Course layout is time consuming, but my specific directions have proven to work well. On one course, I laid out the flags according to my measured and recorded points with no problem. In another race, an experienced coach laid out the flags according to my highly detailed record. He said it was no problem doing this. The race times indicated to me that the distance as run was most likely accurate.
I am seldom certain that any race will lay out a course properly. A big national race here in D.C. made an error in the course a few years ago. The Marine Corps Marathon notoriously laid out part of the course incorrectly one year. Bob Thurston and I make corrections to the Army Ten-Miler course layout every year before the race start. I believe having very specific instructions of where to place course flags every several yards can result in a course that is actually more accurate than a comparable road course because of the additional documentation.
While the work involved in the measurement and the recording is non-trivial, I have set my fee accordingly and my clients are happy with the product. I think the concept of offering certified XC courses could be attractive to runners and to race directors. I am interested to hear opinions pro, con, or sideways.