I went the Handirack Inflatable & can not fault it.
www.handiworld.com/handirack/Packs down into a small pouch & affords the ability to put more or less air into the rear rack if the car has an aggressively curved roof. Travel with board bag on. Metal Ring loops.
Had a 12'6 on & not an issue.
If you are tall or have a tall passenger will the inside strap bother you if you are driving for hours ?