where to put Suburban speaker boxes

[jimfulco]

I have a 79 Suburban. I have some store-bought speaker boxes made for 6x9 speakers. Where is the best place to mount these in my truck. I rarely carry passengers in the back seat, and it stays folded down most of the time. I'm not looking for the perfect system, just listenable. I'm only using a small booster amp, 15w. RMS/side, I think. I was thinking about on the front slope of the rear wheel wells, but I don't know how safe they would be, both from cargo & from thieves. Windows are fairly dark, but not opaque. Any suggestions? Thanks