yes…
This is my experience with this set up, YMMV:
W/o straps the tubing will slide across the bar and roll when moderate force is applied. (my tubing doesn’t go all the way across the bar because I have kayak j racks also) The tubing is “tacky” on the bar/boat for lack of a better word. it is not sticky to the touch but “grabs” the bar or boat when pressure is applied.
When I position the boat front/back the tubing “rolls” rather than the boat “sliding” if this makes any sense. However when straps are applied the tubing “grabs” the boat and bar and I cannot move it fore or aft, or sideways. Then with front/rear tie downs it does not move at all. Just drove 200 mi @ 65 -70 mph on interstate with many semi trucks and the boats were rock solid.
Yakima bar covers
One of my co-workers slid 1.5 PVC pipe over his bars and they do roll and make it easier to get a kayak up there on the rack. It didn’t look that bad, a little down home maybe, but not bad.
Indoor/Outdoor Carpeting
Secure with tie-wraps.