Usually type verification is done through schema compliance assertions in soapUI.
My webservice WSDL has a supporting XSD file with all of the data structures and underlying types, that are contained in the SOAP messages, being well defined.
Example:
If I got a response with a body of:
<Foo>600</Foo>
then somewhere in my XSD there should be something that says what the restrictions on what can be the value in my Foo element, such as:
<schema>
<!-- other stuff... -->
<simpleType name="Foo">
<annotation>
<documentation>
Bar
</documentation>
</annotation>
<restriction base="decimal">
<totalDigits value="6"/>
<fractionDigits value="1"/>
<minInclusive value="0"/>
<maxInclusive value="99999.9"/>
</restriction>
</simpleType>
<!-- other stuff... -->
</schema>
I've also found
Scanner to be a useful class for verify types within strings.