I've yet to come across any coding that eBid prevents you from using. In some respects I feel they give too free a hand. It is not a good idea to mess with the <body> tag as it affects the whole page - not just your description.
The eBid listing page width is 980 pixels wide. Best to stick to that - or centre it (e.g. style="width: 600px; margin: auto;") if you use a narrower width.
If you don't need anything in the header section (e.g. links to external CSS files) then only copy the code from between (but not including) the <body> and </body> tags and paste into the Plain HTML Box editor. You can switch back and forth between the Plain HTML Box and WYSIWYG eBid editors if you use this method.
If you include and need the header section, don't switch to either of the WYSIWYG editors as they will strip it off. The WYSIWYG editors also removes empty elements - so watch for that if you use such elements for layout.
I enclose my templates in a relatively positioned wrapper <div> element. Something along the lines of:
HTML Code:
<div id="ast_wrapper" style="width: 980px; position: relative; font-family: Arial,'DejaVu Sans','Liberation Sans',Freesans,sans-serif;
font-size: 0.8em; color: #fff;">
</div>
This suits eBid's page layout. Plus setting the wrapper element to relative positioning allows the use of absolute positioning of elements within the template. This enables you do do things you couldn't do otherwise, due to the absolute positioning of elements then being referenced to your template rather than to eBid's page.