Click the link below, it's very detailed and will give you greater confidence. Do NOT have the dealer install anything. Perhaps a fellow forum member could help you.
I too bought the gas cap and lower grille insert. I haven't received them yet but I've done two chrome gas caps in our previous H2's. It helped to have step by step pictures like what Crisco provides.
As for the lower grille, why is it so difficult? You're getting me worried!
Crisco's Install Instructions