There are many ways SubmitFeed method can be used. Bellow is how i used it for price update:
<cfset signStr2 = "Action=SubmitFeed&FeedType=_POST_PRODUCT_PRICING_DATA_">
<cfsavecontent variable="prodXML"><?xml version="1.0" encoding="iso-8859-1" ?>
<AmazonEnvelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">
<Header>
<DocumentVersion>1.01</DocumentVersion>
<MerchantIdentifier>#this.merchantID#</MerchantIdentifier>
</Header>
<MessageType>Price</MessageType>
<Message>
<MessageID>1</MessageID>
<Price>
<SKU>#arguments.sku#</SKU>
<StandardPrice currency="USD">#NumberFormat(arguments.price, "_.__")#</StandardPrice>
</Price>
</Message>
</AmazonEnvelope>
</cfsavecontent>
<cfset var gn = GenerateSignedAmazonURL('POST', 'mws.amazonservices.com', '/', signStr2)>
<cfhttp url="#gn#" method="post" useragent="1SmartSolution MWS Component/1.0 (Language=ColdFusion; Platform=Windows/2003)">
<cfhttpparam name="Content-Type" type="header" value="text/xml; charset=iso-8859-1">
<cfhttpparam name="FeedContent" type="body" value="#prodXML#">
<cfhttpparam type="header" name="Content-MD5" value="#ToBase64(BinaryDecode(Hash(prodXML), 'hex'))#">
</cfhttp>
Hope it helps.