I tend to lock my carry gun up in there when I end up somewhere I can't tote it. However, I've recently bought an old PA-63 and retuned it. Once I get a chance to test fire it more for reliability, I may stow it in my vehicle. Effective, and not too expensive should something happen to it.
Alternatively, I've been considering getting another Mosin Nagant, or cheap surplus rifle, to store under the seats. One never knows when a rifle could prove handy, right?