1. Consider mapping all your WorkOrders/Wrappers by a combination key (i.e UniqueKey__c + '.'+ Work_Order_Sequence__c.leftPad(10, '0') ).

2. sort your combo key list comboKey = new List(mapWO.keyset()); combokey.sort();

3. iterate through sorted combokey and create a new list of WorkOrders/Wrappers.

   LIST wo = new LIST(); for (string k : comboKey ) wo.add(mapWO.get(k));

should not need the to implement comparable since you are converting to padded number and can just leverage the standard alpha sort.

1. Consider mapping all your WorkOrders/Wrappers by a combination key (i.e UniqueKey__c + '.'+ Work_Order_Sequence__c.leftPad(10, '0') ).

2. sort your combo key list comboKey = new List(mapWO.keyset()); combokey.sort();

3. iterate through sorted combokey and create a new list of WorkOrders/Wrappers.

    LIST<WO> wo = new LIST<WO>();
    for (string k : comboKey )
    wo.add(mapWO.get(k));
   

should not need the to implement comparable since you are converting to padded number and can just leverage the standard alpha sort.