Exterior dash cam for rear view?

I have Garmin dash cam in our cars our toad was hit (not while being toad) in the rear on icy roads, it totaled the car. The video made short conversations with insurance and police.

Iturn on my lights and the unit turns on. So if I am in a situation where I feel it is needed,on goes the lights and voila-on goes the camera.

As much as I'm not 100% on board about having them in y semi, we have LYTEX/Drive Cams in our trucks w/ cams that face in/out of windshield. They are always on and record things instantly w/ sudden braking, stopping etc. Have heard it goes back 15-25 days or so. Not sure if they have anything exactly like what you want but may have to check w/ them to see. Otherwise, bgums suggestion on the GoPro maybe your only choice.

Not sold as dash cams, but many of the security cameras sold for home use are weatherproof, battery powered, with a card slot for memory chips. These typically record 24/7 as the first sign of movement in an "event" is frequently too late to record the critical details.

For example clicky

GoPro with extra memory. Depends on how long you want to save recording.