Need Sponcership Cover letter, I have made the Proposal

I need to write a sponcership cover letter for a music show which is help every weekend. I have already made the proposal so i need the cover letter to be very short and very formal. My CEO will be signing the letter so i need it to be extra professional. Most of the letters i see on the web have phrases like "Are you intrested". Also, they are way too long and has information which is already in the proposal...

So please anyone has a sample? A short and professioanl one! plz?