Should I cover open space in base rack profile left after ski rack?

[mlt]

I got VW ski/snowboard rack to mount on my existing VW base rack. Ski rack is shorter than the base rack. Therefore I have a couple of questions. Should I center it or can I secure it closer to driver's side? Should I fill open space in base rack profile with a piece of rubber that I had to take off in order to slide in ski rack? I'm afraid that precipitations can do a bad job. I already noticed that black paint from base rack mountings came off in some spots.

[Deserion]

What carrier bars are you using? Thule? Yakima?

If you're using the Votex (VW) bars, they're aluminum.

[mlt]

Yes, I'm using VW aluminum bars. But, there are at least two holes at each end. Through these holes I can see non-aluminum bolts. Also mounts for aluminum profile (that are hidden behind plastic) are non-aluminum and the paint peels off from it.
I'm just curious what others do. Perhaps I can just give up on it. But I don't want to discover rusty bolts by the spring. I'm also hesitating to cut rubber covers from base rack. I'm not sure if I can get replacement.

I'll take pictures later.

[mlt]

Here are the pictures. The rubber thing is actually as long as base rack. I'm not sure if I can get spare if I cut it into chunks.
Can I move ski rack all the way to the driver's side? Or will it influence aerodynamics? On all possible pictures it is in the center.
Sorry, if I ask silly questions:-)