I just carry 2 at a time, it's only 80 pounds but I've found that one 40 pound is hard for me to carry like a baby and when I carry it on one side it hurts my back.  Carrying the two, one in each hand by their carry loop keeps my back aligned and I usually only have 4 to 5 trips.

My comment about nobody offering to carry these to the basement was just the humor I find that these people think I need help to get it a bag or piece of lumber into a cart but never consider I have to get it into my truck and then somewhere from there to storage when I get home.  Even more humorous is sometimes the guy who wants to help is less capable than me.