If the gun is securely holstered, in a way that it won't get banged around or have things bouncing on it as you drive - which it should be - then either should be fine. However, if you plan to leave it in the truck all the time, and you are in Colorado, then you could still have issues with corrosion caused by regular sweating of the gun, or with lube gumming up in extreme cold, with a revolver or with a Glock.
Personally, I think the concept of a truck gun is unwise. I like the guns I may have to use in self-defense to be the guns I practice with the most - that way i know not only that they work, but I have my grip and trigger pull burned into subconscious memory.
Also, unless you rig some kind of under-steering-column holster, or between seats holster, the gun will not be quickly available. If you rig such a holster, the gun is easier to steal, unless you move the gun from a more secure storage container to the holster when you drive - in which case you are manipulating the gun at least a couple times a day. If you are going to do that, why not just get a carry permit and keep the gun on your person? That way it is available, and much harder to steal.
Meanwhile, if what you wanted was a truck gun, why were you even considering a Colt DS? Those things are no longer made, and are continually going up in collector value. A DS is exactly the sort of gun I would not use as a truck gun - if I wanted a dedicated truck gun...
Then again, I just keep a gun or two on my person, and those guns are taken to range sessions and IDPA shoots on a regular basis.