PVC pipe holder/carrier has worked very well. I made it just long enough so that there isn't much slop room for the rebar to move..... maybe an inch lengthwise. With 5 sets of stands in there, it does get to be a heavy bitch! On the other hand, it makes for a nice compact package for hauling. I also make a point to tie it into the bed so it isn't rolling or sliding around.
Making the pipe nipple rebar holders was pretty easy to do too. Having done a few, I won't be buying anymore welded ones....... Not that those don't work well too, it's just that I can buy the fittings, and assemble myself for much less coin.