Disclaimer: I followed the steps below and printed on a Brother HL-3140CW series color laser printer using the custom feed tray for the envelope. You may need to make adjustments for your printer. I found it best to just print on normal Letter size paper first while setting up and once it appeared to be correct then I used the custom paper feed for an envelope and printed.
CREATING TEMPLATE
Create a new Google Doc
Go to File - Page Setup
Set Orientation to Landscape
Leave Paper Size set to Letter (8.5" x 11")
Set Top Margin to 2.5
Set Bottom Margin to 0
Set Left Margin to 1.5
Set Right Margin to 0
Click Ok.
Add placeholders for both the Return Address and the Mailing Address.
Note: You probably want to indent the Return Address one tab so it doesn't print right on the edge of the envelope.
Name your document.
USING TEMPLATE
Open your new document (envelope template).
Go to File - Make a Copy
Then name this new version for this specific envelope you want to print.
Make adjustments to the Return Address and Mailing Address as needed.
Then print and you're finished.
