Did you say that I can use Rustoleum as a top coat for my White bedliner?
If you are referring to a spray can product, you “might” be OK with Rustoleum, but we would very highly recommend automotive paint applied with an HLVP or similar sprayer. It would not be terribly expensive, and would be a more professional job. You could probably get a quality polyurethane from your local paint store less expensive than auto paint. Just be sure it is not a water based product Water based products don’t adhere as well or have the same durability.
We have an aliphatic polyurethane in clear, which can be color tinted white or other color. This single part product is what we would recommended as a top coat to keep the White color. You can call us at 855-545-4900 for more information and current recommendations.
If you are referring to the oil based enamel, Rustoleum or similar can be used with our clear products as a color tint, but not recommended for a top coat. It is too soft, too slow in drying, not durable enough, and does not adhere very well. All those things except the slow dry can be compensated for when adding to our clear, but it is not durable enough for a coating.
Before applying any top coat over sprayed on coatings, wash off or wipe down with mild solvent, any oily surface (if present from amine blush as mentioned). If much over 24hrs, you may want to consider a light scuffing if the surface is glossy. This usually depends on the texture you applied.