I've been catching up on the group after a busy month, so I'm a little late in on this, but for what it's worth...

I agree that the lifter patches look like a bit of an after thought. My solution would be to try the following...

Cut a long strip of ripstop, 2" wide
Fold in half along the length...
Fold the long cut edges in to meet the first fold.
Stitch down both edges, effectively making a long 4 layer strap of fabric half an inch wide...
Cut 3" lengths off and stitch firmly to two layers of ripstop, cut to the size required for the patches... Use a small 'box stitch' - i.e. sew a small square on the tape to hold it to the fabric patch. No need to try to turn the ends in. This will give you a fabric loop to attach the guy lines to, rather than Ray's thread loops, which look kinda flimsy and will abraid you guy lines far more than the loops.

Sew the patches in place. For extra strength, sew an extra patch on the INSIDE of the tarp as well as the double layer on the outside. Use a 2.5mm straight stitch about 1/4" in from the cut edges of the patches, and just go round twice. Use a roller foot, or the walking foot/pin feed mechanism you have built into that Pfaff. If you try to zz such fine, slippery fabrics, you WILL have trouble. Using too many stitches too close together will just create a 'tear here' line in the fabric. You need a good compromise between strength and over-doing it to the point of creating a new weakness. Coated ripstop doesn't fray easily, but if you are concerned, some Fraycheck or seam sealant along the cut edges will glue them together nicely.

You couls pin the patches in place to hold them while you sew, but to minimise the holes in the tarp, truy a quilter's basting spray glue.
_________________________
Kate XXXXXX
Mad sewing witch!
http://www.katedicey.co.uk