While it is safe to leave the rifle with the pellets and projectile in the truck for the whole season, consider this... ever get into your truck in the morning when the windows were up and notice that the inside of the windows are frosted or wet with humidity? Now consider that same thing in your rifle barrel. Humidity is the enemy of black powder.

The one reason I unload my rifle every night is I had two bad experiences with leaving them loaded. I followed all the guide lines, put them on cloth muzzle end down, left them in the same temperature as I hunted with them, all that. And when it came to crunch time, the primer/cap went off and there was no crunch.

Then again, I have friends that do just what your talking about. They take the primer off their rifle, put them in a case, and leave them in the truck the whole season and never had a problem with the rifle going off.

One thing to do before you store it overnight in the truck, take a rag with a little oil on it. And wipe the moisture off the outside of the rifle and prints off it. It will keep it from rusting on the outside.