Just wanted to update this, I posted above regarding concerns about the OM-3 ports and the relatively insecure covers and weather sealing issues. I did get a reply back from OM on this:
"Regarding your question, the OM-3 is designed with internal seals against dust and moisture, including in the connection port areas. The main function of the external covers is to protect against direct ingress of water, dust and debris. However, weather protection does not depend solely on the rigidity or closing force of these covers, unlike older models with flexible rubber.
Therefore, you should keep the covers closed during normal use, checking that they are correctly aligned and fully pressed when closing.
The OM-3 is designed for use in harsh conditions, including cold and humidity, and we want to ensure that you have complete confidence in the equipment."