I use my GoProHD with the Snake River Prototyping lens regularly, meaning several times a week lately. So far the deepest we have gone together is 145 feet. (Yes im a bit obsessed with diving but I live in diving paradise!)
I cant comment on other solutions, but I feel that Snake River has the best offering. They solve three problems blurring, color loss, and humidity buildup between the lens and the flat glass. I have yet to have a humidity issue - the little balls really work (inside the filter holder)
As far as the latch on the GoPro, I actually kicked it open while descending the other day. (I sometimes have my camera mounted on a 5 foot "wiffle pvc pipe") Fortunately I think I was so deep that the back did not open. I gingerly relatched the latch back, and said a little prayer. No flooding. I agree that the latch is not very safe at all. Now knowing this we should all be extra careful. It sounds like some rubber bands might be the duck tape solution for now. I should point out that I did not have the LCD back on. I wonder if the extra weight of the LCD caused your door to swing open on its own once the latch was open?
As far as which "mount" I primarily use two different ones.
For Wrecks, I use a 5 foot 1" thick walled PVC pipe, with hundreds of 1/4 inch holes drilled in it. On the end of it I have attached the GoPro optional standard tripod mount (it costs like 7.00) and bolted that to the end of the pipe with a stainless steel bolt and washers. In addition, I added some JBWELD to the joint between the stand mount, and the pipe for extra security.
For reefs, or when I need my hands free
I use the actual mounting base that the GoPro ships on, and I have drilled it out on either side to allow me to hook a retracter to both sides of it, and wear it firmly against my chest. I purchased the accessory mount kit, and in there was an extra long mount, that allowed me to mount the Gopro onto the shipping plate, and turn it so that it would be flat parallel with the plate.When I want to film, I simply grab the camera and pull it forward, when I am done I let go and its back on my chest. If you have tech gear with a harness you could add a third retracter for more stability. I just leave it filming on my chest as it is actually pretty stable there and sometimes catches things that I would have missed. This setup works surprisingly well. I was worried that the retractors might hurt my back, but they do not, and they do a great job of holding the camera firmly in place.