I have a custom object called Server_Order__c used in my customer portal which is mirrored to the Opportunities object, as well as mirroring the data I would also like to mirror any attachments that are uploaded.

A 'Service Order' object is a child of Opportunities object, each record contains a Opportunity__c foriegn key.

Here is my apex trigger as of now, but it does not seem to work.

trigger CopyAttachmentstoOpps on Attachment (after insert) {

    List<Attachment> insertAttList = new List<Attachment>();
    
    for (Attachment att:Trigger.new) {           
        String parentIdString = String.valueof(att.parentId);
        Service_Order__c oppId = [SELECT Opportunity__c FROM Service_Order__c WHERE ID = :att.parentId];
        system.debug('The ID is' + oppId);
        
        Attachment b = att.clone();
        b.parentid = parentIdString;
        insertAttList.add(b);                 
    }            
}

EDIT
My initial code has a trigger on Service Order updates, however the way Salesforce works when an attachment is uploaded it is stored in a child object hence no updates are made to the parent. I have modified my code accordingly but I am still unable to get it to work.