If you're looking at a Truck Vault, you're probably looking to carry quite a few guns. I've got a 4 door Ford F-150 and recently looked into DU-HA's under the seat storage. These are pretty cool, and they have one cut to fit two guns. Could be great for those trips to the Club for a day of shooting. You can even lock the seat down so it' can't be flipped up. They are hidden so well though, that I don't think anybody would know it's there just looking in the windows. Better than having gun cases lying on the floor. They are even set up to relocate the jack. My truck has the factory subwoofer under the seat, which they offer a replacement for to make this work, but I wasn't quite ready to go through that hassle just yet.
http://www.du-ha.com/ford_f150_supercrew_04_06.html
Mike