I don't bother with karabiners, just loop the whoopie sling through the gathered end of the hammock, and then loop the other end of the whoopie over your marlin spike hitch.
The trailing, free end, of the whoopie sling acts as a drip run off, if it's not covered by the tarp then a couple of inches of paracord tied to the whoopie sling nearer to the hammock will do the same thing, although I've not had to bother with that so far.
The karabiners are just extra bulk and weight and don't add anything to my mind.
Others may have different views of course but this works fine for me
Cheers, Paul