While I have not done with MLD straps, I have used other straps as templates in the same manner mentioned above: lie them flat and trace around. But, from here you will need to add seam allowances and the thickness of the padding. So, for example, if the shoulder straps are to be 2.5″ wide, and you want 3/8″ SAs all around, and the foam pad is to be 1/2″ thick, you need to add 1.25″ to that original 2.5″ (2.5 + 3/8 + 3/8 +1/2 = 3 3/4). So, cut your pieces at 3 3/4″ wide.
edit to add: because you will only be able to trace the straps so far, don’t forget to add 3″ or so to the open ends so you will have some fabric left to anchor to the pack with.
Good luck finding that highest quality eva foam. Just kidding, but you gotta love corny marketing. I get my 1/2″ foam from The Rain Shed. Not sure how it compares to eva but it is certainly better than the blue stuff found in the sporting goods section at those mega-stores. It’s thicker, sure, but it is also softer and more comfortable. A word of caution, perhaps, about buying foam from TRS: most other suppliers seem to cut the foam hieght-wise, so if you say but a foot of it you will get a 12″ x 36″ piece. From TRS, if you buy a foot of it you will get a 12″ x 60″ piece because they will cut it width-wise like a typical piece of fabric.
Shoulder strap tips, already mentioned above. But I will add that when cutting the foam padding to start with a slightly larger piece and then trim it down little by little until you get a piece that fits. If you want to sew through the fabric, padding, and/or webbing, you best bet is to hand crank if your machine can’t do it. And if your machine can, if it’s a cheaper model doing so might screw up the tension.