I love seeing what people are doing with these great patterns!
My first Mariners Compass was a bit over a year into my quilting career when a quilty friend's DH, who was terminal with cancer said he had always wanted one. I Had a terrible time with the background for my next several MCs. Now I cut the pattern using an Xray film template and do as was suggested earlier, pinning the center only and sewing from there to the sides. As I saw on a Simply Quilts show years ago, the background is on top, held loosely elevated, shifting as I go.
I'll have to start a bit later as I have several "have to's" to get out of the way first.