Is this for drag racing? Because if it isn't, it may be a better idea to go to the strut tower rather than the trunk. Going to the trunk from the main hoop is more of a weight distribution idea for drag racing. These are the only pics of my cage that I can find (mounted to strut towers.)
Pre-dimple die sheet metal of course.
Here's another one, my opinion worse picture though:
Anyway, I would recommend just going to strut tower if you're using for grip/drift. I guess if this is for drag racing then go for the trunk...I'll look at my car tomorrow and try to think of something better for going to the trunk.
-Jared