FYI, the problem with silicone sealants is the adhesiveness. They're cohesive, but not all that great at sticking to stuff. It won't even stick to itself once it's set. Also if you use silicone, it's really a bugger to get it completely off for a redo.
ProFlexRV by Geocel is a product I use. This product is available at Camping World.
You mentioned Lowes or WM availability. Your best bet there would be a polyurethane caulk.
2008 Winnebago Sightseer 29R