What I do every fall as part of "getting ready for winter" for my 05 CRV and 07 Odyssey (can be applied to any vehicle), is to remove all the crap that accumulates on the inside of the wheel well lip (rear). Get a pair of work gloves and with your fingers run them along the inner lips to get all that crap out. Once I've done that, I have this product called "Fluid Film". It's a lanolin based rust inhibitor that I spray on the inner well lips and also at the juncture where the rear bumper cover joins to the steel quarter panel. For the CRV, the well lips are plastic but there's tons of crap where the plastic wheel well meets the steel quarter. If you do that type of clean up 1 - 2 times per year, you pretty much eliminated the risk of having rust come through your rear quarters. You may need to touch up the outside well lip with paint once in a while. I also use fluid film through the door drains (spray it all inside the doors) and also all along the outer surface of the bottom of the doors/rear hatch where the drains are.