One of the ways to mount needlework is to lace it over your frame. As cjsews says, start in the middle of opposite sides and lace out to the edges, then do the other direction. This leaves no chance that your piece touches any metal that could rust on it. Use something about the weight of number 8 pearl cotton in white or neutral. This means you need a fair amount of extra fabric around the edges of the actual design so that your stitches have enough "grab" not to pull out.