[gkainz]

I've been across US 40 a bunch on hunting trips and RV trips with a 28' class C flat towing a jeep, and more recently my 25' 5th wheel and Dodge Ram 2500. It's not a bad road in my opinion, but I've spent my whole life towing in the mountains. My mother in law and her husband came down that same route last month in a 36' class A gasser and Honda Accord toad without issue and they're flat landers.
However, winter is unpredictable in the Rockies, so plan accordingly. Watch the weather, have chains and know how to install them and drive with them, or be prepared to wait out a storm. Berthoud Pass from Winter Park to I-70 has steep parts, more on the south side, but is mostly 3 or 4 lane and very good road. Use the slow lanes, pay attention to the recommended speeds and you should be fine.

Do NOT get suckered into taking CO 9 from Kremmling to Silverthorne - it's got a big chunk of highway under construction for the foreseeable future.