Pretty tough unless you have previous military F/E or loadmaster experience. All the VR squadrons I was with preferred to "grow their own." They tended to come up through the ranks...F/A to LM to F/E. A lot of consideration goes to the rating of the Petty Officer involved. An AE, AD or AM had a lot more chance of making it than a YN or an SK.
That said, we did have a YN1 loadmaster in one of my squadrons.