Experience with roof bag?

[Moncha]

Here's a link to my mods page on my personal site.

When the Load Warrior is not on, which is most of the time, here's how mine is stored.

[driver3]

I use the Thule playpen, I really like it. Usually it holds the spare and my thule snowboard attachement. fits the factory roof bars fine, and comes with the locks included (although the factory rack does NOT lock to the roof). I don't have enough room either, mine is now a two seater again and I still feel like I have no room. I'm buying some webbing soon and I'm going to sew a net to connect behind my seats to keep all the crap from coming up front when I stop fast...

[Triathlete]

I use a bag on my factory rack. It works fine, keeps everything dry, is easy to store but you have to put all the soft stuff on the bottom just to make sure you don't damage the roof. I think I got mine at Target for like $30.
As for keeping things out of the front seat during "evassive" braking...tie down straps work like a charm!