I've been through this a few times with a selection of EV's and I had a heated battery compartment for my last two EV which used lead acid and then early lithium.
Any EV should really have the cells in a weatherproof box in one secure location if possible, this should be pretty high on the design criteria from day 1 of any planned conversion IMO. If you have decent "Kingspan" insulated weatherproof box your don't need huge amounts of power to heat the batteries, certainly not 60W per battery.
The system you implement should be capabale of heating or cooling as reqd as all cells have an optimum temp, I aimed at 20-25C with lead and 25-30C with early lithium.
If you look at the pics in this link you will see I used a huge area for battery storage but I was able to keep the temp of that well controlled and power consumed max was about 80W for the entire thing using a disssembled old electric blanket and a habistat vivarium temp controller.
Even in sub zero temps batteries could be kept at my target levels without huge increase in power consumption.
http://www.solarvan.co.uk/ac1.htm
Shows clearly 'Kingspan' cell sandwhich
http://www.solarvan.co.uk/habistatpulse.pdf
Also when I was using lead acid I had this box which had kingspan underneath and an electric blanket under the cells. When needed during coldest periods I could also lower a kingspan cover/box over the whole unit, snug as a bug in a rug.
www.solarvan.co.uk/pbbox.jpg
Basically insulated boxes fitted with thermostatically controlled electric blankets/cooling fans is the solution IMHO.
And just found a photo of my first lithium insulated box here
www.solarvan.co.uk/oldlithiumbox.jpg
It would be a simple Picaxe project to make temp controller with relay or mosfet outputs to control a battery heating/cooling system. An 08M picaxe consumes a miniscule amount of power as well, and you could even have a 16x2 fancy lcd temp display if you wanted.
Bare project estimate <£10 + lcd £15.00
That could be a useful community project with someone perhaps knocking out a pcb
I'm not volunteering at present
too busy.