Request letter is written for asking help. It should be written in polite tone and should not sound like you are imposing or overbearing.
Start your letter by informing the reason of you writing the letter and then make the request for what you have written. You can be clear and straightforward for what you want.
Request letter should be short so that you don’t waste the readers time and request with reasonable limits.
Though you must thank the reader for their time and effort, do not thank them in advance for what you expect from them. This can seem very presumptuous and may irk the reader.