I've been looking at the front again and have a gut suspicion that it is front closing. It is very hard to see, but two clues are a missing loop in the centre front neckline could indicate a centre front opening, or on the right of the picture you can see some piping coming up from the waistband that might indicate that it opens on the side near the left sleeve. This then brings up the question about the neckline trim...
Last night I spent the evening hand sewing the trim and have pictures below of my progress. I have changed my mind about the neck trim and simply cut a piece of striped fabric on the bias, traced my curves on with tailors chalk, and then sewed the piping onto the fabric.
And lastly, here is a picture of my matching bonnet and parasol to be used with this gown. Sorry, its not such a good photo as it doesn't show the fringing on the parasol.