The best way for your HTML emails to get into Gmail inboxes is to use an email service provider. You can use a free email service provider like Mailchimp for example.
If you don't want or just don't have an ESP to send emails, here is what you can do.
Simple method without tools (might brake the email)
Export the HTML of you email (zipped or not)
Open the HTML file in a web browser
Copy-paste the web page into Gmail's editor
2. With using add-on (less rendering issues)
Export the email template from Chamaileon by generating the HTML code.
You'll need to add this Chrome add-on to be able to edit HTML in Gmail.
When you compose a new message in Gmail, ''Edit HTML'' option will appear
Click on it and add the HTML code you previously exported from Chamaileon here.
Here is a video tutorial with the Chrome add-on already installed:
Don't try to modify the content or code on Gmail's UI it will lead to design inconsistencies!