Mark,
I don't know about measuring a line like that, I would have a hard time not trying to get the SPR. But whatever measures you want to take are probably mostly for your own satisfaction, since you won't certify it and most XC runners and coaches probably aren't too worried about some of the finer points of ensuring accuracy.
Lyman did a good job with the course he refers to. Although most meet managers won't go in for the kind of demanding specs that Lyman used to create his course, it's worthwhile to figure out a course so that there will be a limited number of definable key points that they can use to lay out an accurate course.
After doing XC measuring and layout for many years, I'm thinking that it's best for most courses to lay the course out and measure it each season, rather than try for a "permanent" route. With some luck you can find a way to set it up during one season and be consistent, but beyond that is maybe a bridge too far.
One more item to be aware of is that a lot of places will frown on the use of paint, so check on that before painting you or RD into a fine or worse!