There are a number of options. The simple - let it ride, it will lose some temp. The pretty easy – use a blanket, sleeping bag, keg koozy, winter coat and throw it over the mashtun. The slightly more difficult - heat water outside, carry inside, mash-in inside, carry back outside for run-off, sparge and boil. Personally, my rubbermaid looses a few degrees over an hour’s time with 60s ambient, not a big deal. I brew outside even in the coldest of temps and improvise from all of the options I listed above. cheers, j
don't sweat it