Hi Chris,
If you are not able to upload the HTML or zip file you can try below steps to achieve the same:
1.) Copy any existing email in Eloqua and save with desired name and location.
2.) Open your HTML file in any HTML editor like Dreamweaver.
3.) Copy the HTML code from Dreamweaver or any HTML editor you are using.
4.) Paste the code directly in the New Email you created in Eloqua. Then click save.
After this, to make your images working you can use the image browser of Eloqua to upload and drag and drop your images in the email.
Upload functionality suppose to work if there is no error in the code. You can raise a ticket in Eloqua Support and they can resolve if there is any technical glitch.
Hope this helps!
- Raj