Preparing lower doors/quarterpanels and fender lips for bedliner.

I am going to be sanding down my lower doors, and my lower quarter panels along with the lips of my fenders to apply bedliner. What do you suggest I do as far as prep? I want to keep the paint up until the lip of the fender, where the paint is already chipping away due to trimming the fenders. I don't want it to chip away anymore. Thanks for the input in advance. Also, any way I can get my fenders to be more rounded and cleaner looking? I will be running fenderless, so I want it to be presentable.