I was just wondering where everyone has installed their sub if they have one. I thought about under the back seats but it looks like they don't come up and no space under them. Any insight is greatly appreciated.

 

Had an 08 Vue for a while.
No, the back seats don't lift up.

I think in the back, on the roof are your only viable options.

Watch out for that 3.5.R waveplate failure. Hope yours failed and got replaced under warranty.
And the caliper pistons that don't retract. If it smells like burning brake pad, it is.
If a pad catches on fire, let the m f burn, You're better off.

One of the smoothest shifting auto trans I have ever experienced -- while it worked

Sweet vehicle when it was problem free up to 100 K. Design flaws Design flaws.
If it's any consolation, the Ford tranny that came out of the GM Ford collaboration 6F series, 6F35 in particular, has some issue with fluid pressure control. Hits almost every escape. Random mileage distribution.