I'm also looking for a minimum 3 camera setup. I need it to keep up to about 2 weeks of video on it before it loops and starts recording over existent video. Would also like shock sensor and GPS, 1080P with night vision. I'm sure you have seen this one. I have no price on it, they say its expensive?. Here is the link, , I know nothing about this company and not affiliated with them. Just a trucker looking for a good camera setup.
336 hours of HD video would require a MASSIVE storage device. You won't find anything in the normal world of dash cams that will do that. And with 3 cameras it takes to over 1000 hours of video. You'll need something with cameras wired to a computer. Check with surveillance companies.