Here's a suggested easy fix for adding spaces in the generated XML where there used to be <br> or <li> that created the line breaks.

Around line 185 of store/includes/classes/google_base.php, replace this:

$str = str_replace(array("\t" , "\n", "\r"), ' ', $str);

with this:

$str = str_replace(array("<br />","</li>","\t" , "\n", "\r"), ' ', $str);

And it will add a space at the end of bulleted lists and line breaks. This is assuming your break tags are formatted the way zencart formats them, <br /> as opposed to <br>. This is because it will only replace those that match the arguments in the list.