A couple of additional thoughts:
1. Some schools prohibit other universities' grades from transferring over, requiring that the credit be recorded as either "Pass" or "Fail." Obviously, that's unsatisfactory if David's looking to boost his GPA in addition to receiving the credit. In that case, he might have to take one of Clemson's online courses, which would carry a grade with it.
2. If he takes a course, he should consider not taking the summer job that his Cape team offers, applying the morning hours to the course. With a number of teams playing 4PM games, the afternoons tend to get pretty "shot" except for anything other than baseball.