Having tried a couple bottle dynamos before going back to my Niterider Moab, I was amazed bt how much resistance the dynamo added when engaged! These were 12V/6W units, so if you were to find a 10W one, it would nearly double the required effort to power it. We're talking about 8amp at 12V to get 10W, which is a very healthy draw.
My solution for touring (though probably not winter tours) is to put a 20W (nominal) solar panel on top of my trailer, to charge an ATV battery, which I can then use with an inverter to power my laptop at night. Of course, I will have a charge controller between the panel and battery. I can also charge different units (rechargeable AAA's, Moab battery, notebook, etc.) during the day while riding.