I prefer towing/driving at night because there are less people on the roads. For me, temperature is not a consideration. I like to set cruise control and not turn it off until I get off the highway. Driving at night generally offers that, as long as there aren't any major accidents. If I'm familiar with the route, I prefer to drive at night.
When we towed our travel trailer with our Nissan Xterra, we couldn't run the A/C because the engine would run hot. If others have the same issue, then driving at night would definitely be a plus if daytime temps are above 70 degrees and the sun is shining.
-Michael