Problem seeing who's behind me while towing a TT

One aspect of my driving any vehicle is keeping an eye on whats going on behind me. I'm not talking about the blind area directly behind my 5er, but behind me down the road. I feel it's important to know what may be coming up on me, especially if it's an emergency vehicle coming up fast. I have seen quite often where a driver is completely oblivious to an emergency vehicle on his a$$ trying to get by.