1. Type the letter on your word processor. 2. Use the word processor spell check. 3. Copy your letter with your right mouse buttton. 4. Enter your cursor on the comment line where you want to put your message. 5. Paste your message with the right mouse button.
If you can open 2 windows at once for the forum and your word processor, that should help too. I hope you find this as helpful as I do, but even I still make plenty of mistakes with my postings.