Do these covers need any prep or paint before install?

They come ready to install as-is. If you want to match interior trim color, light scuff with 220-grit and use spray adhesive rated for plastic. Most buyers leave them black or color-match to their interior trim.

Do I need adhesive or fasteners to mount these?

Installation method isn't specified in the product data. Test-fit first — you may use contact cement, plastic-rated trim adhesive, or small fasteners depending on your door handle design. Handle geometry varies by interior option, so mock-up before committing.

Will these fit if I've already replaced my door handles?

These are molded to factory handle profile. If your handles are aftermarket or significantly different in shape, fit isn't guaranteed. Measure your current handle diameter and geometry before ordering.