Mirror Modifications on a 99 Ford Explorer

OK. I may be towing a TM3023 next week, and I am concerned about the size of the mirrors on my TV Explorer. I've seen ads for "add-on" mirrors for the existing factory mirrors. Does anyone recommend using that type of mirror, or am I going to have to have something permanently installed? I'm already adding the receiver hitch, wd hitch w/sway control, brake controller... just wanted to keep any additional costs down right at the time I'm purchasing the unit. Ideas anyone?