Sorry I must have worded my question wrong. I already know the bars on the car can hold the weight. The issue is that cars bars run longways down the car not across and I'm not familiar with the attachment of the rooftop tent. Do they mount directly to my roof bars or do I need to install a platform or special crossbars that support weight better than the aftermarket subaru aero crossbars?
I'm sorry for the misunderstanding! Now I know what you mean.
Most tents like the one you posted mount the same way -- underneath the tent, there are typically two lengths of aluminum that have special channels in them, and these channels hold a bolt and a plate. To mount the tent, the aluminum channels on the base of the tent need to be perpendicular to the roof bars, because you need one bolt and plate on either side of your roof bar to clamp the tent down, as in this photo below:
The black is the "roof bar", and the silver is all part of the tent -- there is the captive channel and then the bolts slide into that channel through a plate, and that pinches the tent to the roof bar. Below is another view that shows how the bolts are on sliding plates inside the aluminum channel.
SOME (not all) tents allow you to change the direction of those aluminum pieces, so no matter how you want your tent to open, you can do it -- simply figure out how the tent opens, and then mount the aluminum channels perpendicular (i.e. at a 90 degree angle) to your cross bars, so you can sandwich your cross bars to your tent with a bolt on either side and a plate across the bottom as in figure 1 above. If you are unable to change how the aluminum pieces mount to the tent, then you only have two options:
1) Mount the tent anyway, and just accept that it might not open in the direction you want (i.e. it might open off the side instead of off the back)
2) Install cross bars on your existing roof bars to give you a perpendicular mounting surface, however this has the disadvantage of adding height which you may not want.
I hope that is more helpful but I recognize it can be hard to figure out from text and a couple of photos - feel free to post up more questions and I can share more.
