Thank you for replies.
The biggest issues I've been able to brainstorm is
- wet ground = wet feet and potential frostbite overnight
- wind driven snow entering the stock ventilation windows
Are elevated roosting bars enough or will they need a snuggle boxes /rug? Any behavior I should watch for that indicates too cold?
The surrounding farm land means we get some pretty high sustained winds (typically west / NW) so I keep the man door facing east. This keeps the wind loading on the long axis and facilitates closing the top to keep wind driven rain coming while leaving the leeward side open. The solution may be as simple as foregoing the stock zipper vents and installing some baffled roof vents at the top of the gables.
Regarding the greens, the enclosure is 10x20 and I've got 2ish acres to play with. After eleven weeks of moving daily and they have yet to complete a 'lap' of the pasture. On this schedule, aside from the occasional bare dirt spots some of the hens have been digging to cool off, the grass looks completely normal after 4 or 5 days. This is likely aided by my practice of using a rake to stand the grass back up/break up the poo after each move. Early last month I was forced to leave the tractor stationary for 3 days - they did not pick it bare but it was definitely down trodden and sparse. It took three weeks for the foliage to recover, though thanks to the dense 'fertilization' its now the greenest patch in the field.
Regarding the water, I'm hoping the solar gain from the tarp plus 15-20 fluffy chickens will be enough enclosed heat to prevent freezing most nights. If not I guess potential backup plans are lots of toting fresh water, a 12v heat tape/block heater or spending a small fortune on extension cords for standard 110v heating solutions.
Regarding snow - I agree if I was any further north, let alone WI, moving the enclosure would time and cost prohibitive; however, we really don't see inches upon inches of sustained accumulation. Plus I figure If I'm already bundled up and on the tractor clearing driveways for the elderly / less equipped neighbors, whats two more passes to clear the way for a weeks worth coop moves? Between the FEL bucket and 3 point mounted snow blade I've been able to clear some nice grass paths for my neighbor that uses an electric golf cart for the twice daily commute to his barn.