It's pretty easy to do side cams if you have any fixed non-opening side windows, and the B1W is often a great fit when done this way. If you have no such windows things get a little tougher as the cams will have to be mounted in such a way that passengers don't bang into them entering or leaving the vehicle. And as always you must avoid having a cam or wiring interfere with any airbags. Sometimes a Taxi/Uber type cam can give you enough side coverage towards the rear but roof pillars and human bodies can interfere with the view then so it's not a perfect solution. Dual remote cams like the K2S can also be great for side cams, and more than a few people have a 2-channel 'wedge' style cam for side coverage.
Regardless of cam choice here. you're going to get a lot of motion blur with vehicles going in the opposite direction, so if identifying them via the license plate is a high priority that needs to be handled by your front and rear cams, although you can often get a great face pic from a side cam going frame-by-frame in review; it's just not going to always happen.
Kind of sad that we need so much protection from our cams but I agree- with today's traffic I feel somewhat naked without side cams. And only in an emergency will I drive a vehicle without at least a front cam; I have an extra one set up and ready to go with a suction mount and ciggie-plug PS just for that purpose.
Phil