Good Morning!
I took a careful look at the layout and visited some of your active listings on eBay for visual check before starting.
Here's what I've done.....
1) I removed the portion of the description section unique to the sample listing you provided and replaced it with the Auctiva [DESCRIPTION] tag. That was everything from just under the description with shopping cart header image down to the paragraph that begins "Thanks for looking!", which appears to be common to all your listings. You use that tag by creating that unique item description code in the Description box on the one page lister. To start use, just copy that section of code from the sample to that box with the box set to HTML mode.
2) I substituted Auctiva's [IMAGEx_URL] tags, where x is numbers 1 to 24 for the 6 images you had in the sample listing and added code support for the 7th to 24th tags. This give you full flexibility to operate with 1 to 24 images for any listing. I see that your designer was operating that section by adding a space gap between the six pictures. I replaced that method with one that will work better with the tag system. Essentially, I added a margin to the bottom of each image element that will only operate when the image element is used. That way you won't have excess gapping, e.g. 18 extra gaps when only six pictures are used.
3) I replaced the Scrolling Gallery code with the [STORE_WINDOW] tag. If you set your options for the scrolling gallery for it's placement at that bottom location, the tag can be removed, i.e. Auctiva knows to place it there automatically by that option.
Here's the template code. You need to copy the code to the template editor. That's found on the LISTING tab, "Create your own Template" link at lower right on the page.
http://practicewriter.com/vu/?5DE85
Here's the description section code that I removed. You can copy that code to the one-page lister description box to get you started.
http://practicewriter.com/vu/?5DE87
I hope that's good start. Please run some tests with the one-page lister preview for verification and note back any changes on a post.
Oh....once you create the template, you select it in the one-page lister. Look for the blue box. On the selector window, look upper left and select "Custom" to locate your custom template.
Danno