According to PayPal documentation on this the input that is named shipping should hold the value for the total shipping charge when the cart upload is used. This should be the case for you in this checkout.
Do you have any shipping rules defined in your PayPal profile? If so this will override the value that you have specified in this element.
Instead of changing the handling element you should try adding in another one for the shipping, it should look like this:
<input type="hidden" name="handling_cart" id="handling_cart" value="" />
<input type="hidden" name="shipping" id="shipping" value="<?php echo ($megan_isaacs->GetShipping() + $megan_isaacs->GetCharges()); ?>" />
Give this a try to see if you can get the shipping charges to show on PayPal. Also here is a link to the documentation for the Payments Standard: