save camel messages between routes - spring

Question

We use Spring DSL to define camel routes. In one case the message headers disappear.
Our design requires an audit trail to help debug issues, and prove that messages are moving as designed.
We use and reference an audit processor to create a message file name from 2 headers, 1 is constant, the other is a unique variable.
We can't use setHeader in the case of the variable one.
Here is a generic example which includes commented attempts that failed:
<route id="msg_in">
<from uri="direct:msg_in" />
<wireTap ref="audit" processorRef="auditPreprocessor" />
<to uri="direct:to_json" />
</route>
<route id="to_json">
<from uri="direct:to_json" />
<!-- the below seemed to have failed -->
<!-- <setProperty propertyName="SaveId"> -->
<!-- <simple>${in.header.UniqueId}</simple> -->
<!-- </setProperty> -->
<bean ref="JDBCProcessor1" />
<!-- headers still exist here -->
<bean ref="ToJSON1" />
<!-- headers still exist here, and wireTap on the next line works -->
<wireTap ref="audit" processorRef="auditPreprocessor" />
<bean ref="toJSON" />
<!-- Message headers do not get to here so we need to set them again ? -->
<setHeader headerName="Hdr1">
<constant>Update1</constant>
</setHeader>
<!-- <setHeader headerName="UniqueId"> -->
<!-- <simple>${exchangeProperty:SaveId}</simple> ... this didn't work -->
<!-- <simple>${properties:SaveId}</simple> ... this didn't work -->
<!-- </setHeader> -->
<to uri="direct:msg_out" />
</route>
<route id="msg_out">
<from uri="direct:msg_out" />
<!-- we try wireTap here but no headers, saved file is null-null
and gets continually overwritten, so no usable audit trail -->
</route>
I spent considerable time trying to find the right way to do this in Spring xml, but no luck yet.
Thanks in advance if anyone can help.