I have attached a larger version of the passenger foot well fuse box and have circled the PWR/MODING fuse. It is 2A. I verified this both in my manual and in the vehicle itself. BTW, the fuse panel is tilted and a support bracket runs thru it so hopefully, you can orient the picture properly, if it is the same as yours.
Also, I found an online 2008 Vue online manual at:
I remember that my old 2006 Vue said to pull the IGN or Ignition fuse or something like that under the hood. I pulled it while pulling this Vue but the battery ran down after about 5-6 hours of towing. Then again, the 2002-7 Vue was a different animal.
The PWR/MODING fuse, when removed or switched, cuts all power coming into the interior cabin. Unfortunately, this includes the power port/cig lighter. What I did was have a power port installed on the face of the change compartment on the far left side and ran it straight to the battery. That way, I can use my brake assist while towing. This setup has worked well for me. I have towed the Captiva on 3 trips that were between 250 and 600 miles long over multiple days. I had no problems with the battery running down.
I did have intermittent connectivity problems with the umbilical cord between the RV and the Captiva on 2 of those trips. This affected the brake lights/turn signals on the rear of the Captiva. But Blue Ox replaced the cord even though it was out of warranty.
I hope this helps. Good luck to you. Towing behind an RV does present various challenges.