No problem. I run double stacked 32' and 24' long distances, in fact sitting on my roof now, just about to pull them off. I've run a 40' up there a few times.
I added 2 extra factory cross bars, so 4 total. The factory roof rack I think is rated for 160Lbs, I've had a few hundred pounds up there before with a serious amount of lumber, haven't bent my roof yet. People camp on top of these things. I use ratchet straps for the bottom ladder and bungee the other on top. For the 40' I also take ropes and tie off on the bumper D rings. I've taken some serious crosswinds and holds tight driving 80mph.