Count on the trip taking at least half again as long as the same drive without the tow... You'll really need to be concious of any hills, corners, and as Bob T said, lousy driving conditions.
Even if things feel fine as you're driving along avoid the temptation to speed up... stay in the slow lane, tap her light and get home in one piece!
Best of luck
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)