You could (and would have to) build insulated battery boxes as well in your situation. These don't dramatically add to the cost of a conversion (insulation and heaters are cheap) but they would add to the volume necessary for batteries.
However, winter driving means more energy used for heat, defrosting, wipers, lights, etc. And you will likely be plowing through rain and (in your case lots of) snow and all this going on at once can impact electric range by 20 to 30 percent easy. AWD will be a 5 to 10% tax on range as well but in your case maybe a requirement.
One thing that might be working in your favor: What kind of speeds are you looking at for that 60 mile (minimum) range? If it is mostly at non-freeway speeds (secondary roads and such) and not too hilly you might be able to get away with a somewhat smaller battery pack than if you wanted that 60 mile range at 60mph. As a real world example, my MR2 can do 50 to 60 miles at 60mph straight and level. If I could drive continuously at 40mph under the same conditions instead (depending on where in AK you live, quite possibly a more realistic situation for you than for me) the range would be in excess of 100 miles easy. This effect is largely due to the square law of wind drag (doubling speed quadruples wind drag) but also in my case there is a factor due to the lead acid batteries and their peukert effect which would be much less pronounced with lithium batteries.
You could also consider a smaller vehicle. As for towing, a "small" boat is a relative term but assuming no more than 2 or 3 thousand pounds there are smaller vehicles that would still seat 4 and tow the boat after being converted.
If you do have significant hills, then with the towing requirement an AC drivetrain might be very well advised for the Regenerative Braking
ability. There is no "engine braking" in the typical DC powered EV. At the very least, ensure the boat trailer has brakes.
I am starting to theorize what my second EV is going to look like, and I want it to be able to seat 4, tow around 2000lbs and have decent cargo space. In other words, similar to what you are thinking. FWIW here is my very preliminary plan: I intend to use a solectria AC55 for the motor with direct drive using around a 6:1 gear ratio, and enough batteries for a 100 mile nominal range at freeway speed (at least 30KwH usable) My very preliminary current list of candidate vehicles: Pontiac Aztek (the heaviest but also with the most fat to lose up front, and also my favorite at this point), PT cruiser, Chevrolet HHR, Mazda 5, Scion xB (by far the lightest). I am expecting to be spending around $25K on the build, mostly for the batteries. I already have the motor and inverter (lucky craigslist buy) and I will recycle the manzanita charger from my current car.