If paint is coming off, you don't want to spray anything over it, as it will just come off as well much sooner than it normally would.

You may want to pressure wash off whatever is loose, even light sand the area down. You can then hit it with that Undercoating spray to protect the metal. But also, a set of rear wheel well liners is a better idea and a great investment. Not hard to install, even with wheel still on, and it offers better protection than anything, as nothing touches the metal. It is a good idea to pull the liners at least once a year and clean out behind them, as some stuff will still get in, but it won't be that bad.

 

like mentioned above prep will be the key to longevity. Clean the flakes and sand good to remove the surface rust then spray-a-way.. I have used that brand before and i had no issues with it, gives a slight roughness to what its sprayed on.

 

I like the idea of the wheel liners...didnt even know they existed.

how about these from amazon?

Husky Liners Rear Wheel Well Guards Fits 07-13 Silverado/Sierra 1500
by Amazon.com
Learn more: https://smile.amazon.com/dp/B00JH5O4OW/ ... PCb6JQ1GK9

thx!

 

If the paint is flaking then it will start to rust eventually. Wheel liners will just hide the problem.
I would sand it down, use an etching primer, and either use bedliner yourself (with proper prep as instructed on the can/bottle), or have LineX spray them. I think rear wheel wells can be LineX sprayed for about $150

I used a product called Herculiner on my rear wheel arches as well as the underside of the body behind the rear wheels and it has help up to 2 years of daily off road with heavy heavy mud kick up

 

With it just flaking and not rusting, I would look into getting it Line-X'ed or RhinoLined black. They will do the prep work, it will stick, it will help to keep the bed rust free and it will look good.

 

The stuff in the can will come off in about 1.5-2 years as well i speak from experience. I used it.

 

I'll second the liners. I just put some on my 2012 and they look and fit great. Installed in about 30 minutes without removing wheels!

https://smile.amazon.com/gp/product/B01016XVL2