Magento XML layout with custom modules

I'm trying to include a custom template into the checkout process on the shipping page. I want that template to adopt the functionality of its parent template so I can use any of the shipping variables within the template. However I can't get magento to load the template. Here is my XML (the header scripts are adding successfully). My module is called Tm_ShippingDate

<layout version="0.1.0"><checkout_multishipping_shipping><reference name="head"><action method="addItem"><type>js_css</type><name>calendar/calendar-blue.css</name><params/><!--<if/><condition>can_load_calendar_js</condition>--></action><action method="addItem"><type>js</type><name>calendar/calendar.js</name><!--<params/><if/><condition>can_load_calendar_js</condition>--></action><action method="addItem"><type>js</type><name>calendar/lang/calendar-en.js</name><!--<params/><if/><condition>can_load_calendar_js</condition>--></action><action method="addItem"><type>js</type><name>calendar/calendar-setup.js</name><!--<params/><if/><condition>can_load_calendar_js</condition>--></action></reference><block type="tm/multishipping_shipping" name="tm_shippingdate" template="tm/shippingdate/shippingdate.phtml"></block><!-- <block type="checkout/multishipping_shipping" name="checkout_shipping" template="checkout/multishipping/shippingdate.phtml"> --></checkout_multishipping_shipping>

I then have this in my checkout shipping.phtml template

<?php echo $this->getBlockHtml('shippingdate') ?>

Thanks