So after sitting on the shelf gathering dust for longer than I care to remember, I have made some advances towards completing it.
It does not have as much stowage added to it (and the base model was completed before Rubicon brought out their German Stowage set). An HO scale oil drum with added straps and filler cap has been added to the right hand track guard. A box from the Warlord plastic Universal Carrier has been added to the left hand track guard together with a jerry can probably from the Warlord SDKFZ 251C kit.
One feature of illustration of the Cromwell is the presence of the squadron identifier on the boxes either side of the turret.
None of the decal sets have one of suitable size, so I decided to try and use the very small invasion stars from the original Rubicon M5A1 kit. I cut out the star in the ring and then cut the star out of the ring.