Any way you can make the front tower bars lower than the back ones? No reason to carry the heal-piece clearance all the way through... this would also lower the tips on the top skis away from your jugular.
Not only would I get bungies to secure it, but I'd wrap them in something.
I rolled my rig twice. (it was a big rig- '72 blazer) the first time, my 3ft x 2ft x 2ft tool box from the back cargo area ended up in the passenger seat. there was only 2ft of clearance between the seat and the roof, not to mention I rolled and flattened the roof. How it got to the passenger seat is beyond me. Both times I rolled it, I was occupying all livable space after the roll.
I like your rack, it's clean. But I'm a paranoid driver now and probably wouldn't feel comfortable riding shotgun with those skis like that. I say- package them up! Build a housing to shell the rack you made.
at least you're less likely to roll in your subie than a van. (or a '72 blazer)