Originally Posted by tbctx
I think normally people just overlap them such that they can control where the water goes without any actual joining as the joining would be extra weight for a normal set-up and/or potential damage to a tarp.
I agree - its far easier to not actually combine them, just creatively hang them. That said, if it were me and I had to, I'd prefer to use rope and lash them together (maybe put in some grommets along one edge of each tarp and use rope to tie them together). I wouldn't trust tape or velcro in gusty winds - rope and knots seem much more secure.