If you really want to go bare bones on your email template for Soapbox Mailer, here's a very blank template you can use to keep it nice and simple. Really, really simple!
<html lang="en" xml:lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>{!Campaign.EmailSubject}</title>
</head>
<body style="font-family:arial;">
{!Campaign.EmailBodyHTML}
</body>
</html>