So I have a Remington 870 tactitcal (the one with the magpul furniture) and am noticing some rust starting to happen to the slide rails where the pump handle rides along and the top front XS big dot sight. Anyone else have this and how do I prevent it from further rusting?

Id say get rid of the rust thats already there with a soft brush and oil that baby!  It could also be where you are storing the gun.  Hot to cold and humidity can do it.  Store in a cool, DRY place and keep it oiled. 

The newer 870 are known for rust problems with the blueing. The last one I got was rusted right out of the box. I'm getting it Duracoated in camo so its not really a problem for me. 

Get some break free CLP. Take the shotgun apart and soak the parkerized parts and let it sit for a bit. the parkerized finish will absorb the oil and help prevent any further rust. 

Keep a light coat of oil on all metal surfaces almost wet to the touch(i've had great luck with CLP.. The old stuff) maybe store it in a gun sock too....youre not the only one so dont feel bad.. Our 870P's at work are rusting too out of the box..

Thanks guys....I noticed a tiny bit of rust on it out of the box...took it out recently to get to other guns to go shoot and noticed it started spreading.