I used the BPL NANO Dyneema guyline kit to make the lines for my SMD Gatewood Cape. I cut the lines to 24" and then used about 3" to make a loop on the non-tensioner end. Rather than using the micro-biners I simply pass my loop through the tieout and then pass the tensioner portion through the loop. I leave them attached if I'm not expecting rain or remove them if I'm likely to see rain.
The Gatewood Cape also has an extra tieout that allows you to create a little additional headroom for which I have a 60" line – you can see it (thanks to other BPL members) in the photo below:

The cord is very tangle-resistant and, when they're not attached, I keep them with the harness in a snack-sized ziploc bag.
Good luck – just remember that a 12" line does not allow you to have a 12" gap between your tarp and the ground. You're always going to stake your lines at an angle and, if you have the micro-tensioners you'll further cut your length in half by the distance between the stake and your tensioner.