[Ryland]

You should be able to get your watt hours per mile down below 300 if you never drive over 25mph, but I bet that is not what you want to hear.
I agree with Dax, plan for at least 400 watt hours per mile, 500 or more in the winter depending on where you live and how much heat you like, the heat it's self doesn't draw the your range down much more then 10-15% but the cold batteries will reduce your range, I notice my range dropping off by 5% or so at 50F, but a little insulation around the batteries and a few 100 watts in heaters that turn on when the car is plugged in will help a lot, but even then when it's cold it takes more energy for the tires to roll, the air is thicker so that is more resistance, oil and grease is thicker and then the batteries are cold on top of that.
Lead acid batteries don't like to be discharged, sure deep cycle batteries handle being discharged 80% but it shortens their life! I figure with a new set of batteries I don't want to ever draw the pack down below 50%, that way when my pack is 4 years old I might be drawing it down to 70% and that 5th year it's being drawn down to 80% to go the same distance, for every day driving tho I am only use a fraction of that, I get to work and my battery pack is between 72% and 78% full depending on the weather, then I plug in, of course the average lead acid pack in a car lasts 3-4 years and mine is on it's 4th year and still and 80-90% of it's life left, so if I keep up with the light use I might get 7-8 years out of this pack, something that is almost unheard of with a lead acid pack in an EV, using it nearly every day 9 months out of the year I have collector plates on the car, ice covered hills going to work so I garage it over the harsh months of winter.