I tow constantly but my travel trailer is 7' wide, the stock mirrors work fine for me no need for extended mirrors.

 

I got two of these to help towing with my small boat trailer. The trailer is small so it is hard to see backing up when empty. These help to see the back of the trailer. They do vibrate at freeway speed but for backing up purpose they work good. I only mount them when taking the boat out.

**** 11950 Clip-On Towing Mirror Black & Silver, 15.75 Inch https://www.amazon.com/dp/B00029WRKA/ref=cm_sw_r_cp_api_i_DCGEW9DX5C49RGF47EZW?_encoding=UTF8&psc=1