2K Seems really high when you can buy a JRC 1500 MK II with an 18" 2kw dome, stand alone unit, for around $1100.00. Beyond that you can install this display at he helm, where it will actually be of some use, and not worry about getting it wet.
Up here in Maine it's critical to have the radar at the helm in thick fog. It's even better to only have one display and have the radar overlayed but you'll run into more cost that way.
When you're in 30 foot vis the last thing you need to be doing is going up and down the companionway to check the radar on a computer screen. I won't even go into the reliability issues of using a PC for anything on a boat...
Most of the commercial fisherman up here use JRC it's not fancy but it's durable and it works. JRC (Japan Radio Company) has made domes for many of the name brands you see out there for years & years..
I suppose if you are only going to be using it for night time use, without fog, than a PC may be OK but do keep in mind that even on the lowest brightness settings a PC will destroy your night vision where a dedicated marine display is designed to be dimmed enough to not ruin night vision.
IMHO PC's & boats do not work well together and should NEVER be relied on as a main source for anything other than surfing the net...
One more thing. A 20" dome, on your boat, is about 2" to 4" bigger in diameter than it needs to be. Keep the weight down aloft and go with an 18" or smaller dome..