Yesterday I made a cheap mount for my Raymarine i70 using a Bud PN-1337-DG water-proof enclosure. This cost $9 from Amazon. The Bud PN-1336-DG would be a little nicer looking and lower profile, but for some reason those are $28 from Amazon.
First I drilled the 80mm (3-1/4") hole for the instrument and 4 pilot holes for screws. I did this on a small CNC mill, but it is an easy job on a drill press:
I mounted it using a RAM ball mount on the back of my seahood (over the companionway). I already had this lying around, but they are about $20-$30:
Note that the case is fully closed in that photo, even if it doesn't look like it. There is an O-ring seal around the inside edge to keep it waterproof.
This is the final product:
You need to take the bezel off of the i70 to get good access to the 4 screws that close up the case.
I like having this instrument mounted over the companionway. You can see it from anywhere in the cockpit and I rarely push the buttons so there is no reason to have this on the pedestal.
I think that this looks nicer than a NavPod and it's a whole lot cheaper:
Navpod PowerPod Grand Prix Series