You are proposing pulling an 8x15ft trailer with a Leaf?!?
Unless the reflector is twice the size of the panel you won't double the output except maybe in one precise solar alignment.
Cd 0.28 to 0.18 is not as easy as, for instance, 0.38 to 0.28; it's close to halving the resistance. But aero is the 'low-ahanging fruit'.
Edit: Not sure where I found this—for sure not the first 24 pages of Guns, Oil and Dirt.
Anyway, if 40mph is your cruising speed:
