The first paragraph should have a brief introduction of the sender of the letter. Be concise and to the point. If you represent a trust or an organization, briefly introduce it as well.
The second paragraph should be the actual reason of writing the letter. Mention the previous activities of the trust and how the money taken in charity will be utilized. Be clear and add the specifications if necessary. Never demand an amount. Always leave it to the discretion of the giver. Always thank in advance. Offer assurance against any misuse.