There is no surface prep needed, you are not actually bonding the ports to the bumper but actually to the inner ring. The assembly is holding the bumper between the 2 parts. This was done to eliminate durability issues as the ports are not the same material as the bumper and obviously need this play to make up for material expansion over time.... The price may seem high, but allot of money was spent in development and tooling to get a part easy to install.
Here are a few pics which could help