Let me throw in my .02...
You an cheat Sigil into putting any kind of code in when you Add a cover. Simply save whatever code you want as a file named "cover.xhtml" into Sigil's default folder. When you add a cover it will use that template if it is available; if not, it uses it's default SVG wrapper.
Here's the template I use:
Code:
<?xml version="1.0" encoding="UTF-8" standalone="no" ?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Cover</title>
</head>
<body style="margin:0; padding:0; text-align:center; background-color:black">
<h1 style="display:none" title="Cover"/>
<div style="margin:0; padding:0; text-align:center">
<svg xmlns="http://www.w3.org/2000/svg" height="100%" preserveAspectRatio="xMidYMid meet" version="1.1" viewBox="0 0 SGC_IMAGE_WIDTH SGC_IMAGE_HEIGHT" width="100%" xmlns:xlink="http://www.w3.org/1999/xlink">
<image height="SGC_IMAGE_HEIGHT" width="SGC_IMAGE_WIDTH" xlink:href="SGC_IMAGE_FILENAME"/>
</svg>
</div>
</body>
</html>
SGC_IMAGE_HEIGHT
SGC_IMAGE_WIDTH
SGC_IMAGE_FILENAME
Are variables that autofill with the properties of the image you select.
It should work just fine with any kind of HTML code as well as it does with SVG...
Cheers,