Here in Zone 6 CT, I dig a broad, shallow hole in a raised bed as a winter home for Sarrs, hardy orchids and various other things. I set the pots in the hole so that the rim of each pot is at least an inch or so above ground level, putting extra dirt under the shorter pots and using dirt to fill in around the pots.
I cover everything with oak leaves. Don't use maple leaves because they'll just mat down, losing their insulation value and suffocating the plants. The best leaves are thick and curl a bit when dry. I take a couple weeks to pile on all the leaves, adding a couple more inches every few days. I end up with 12" - 18" of leaves and pull the Sarr phylodia and pitchers up through the leaves.
The last step is that I put a landscape fabric covered lean-to over everything, to keep snow off the leaf pile. The first year I over-wintered Sarrs we didn't have much snow and everything was fine without the lean-to. The next year we had the normal few feet and the snow would melt a little on warm days and the water would freeze down below. By the time I thought about it, the plants and pots were encased in several inches of solid, leafy ice. I lost some plants and began using a lean-to to prevent that problem.
The plants are frozen under the leaves, but Sarrs don't need to be protected from freezing. They need to be protected from the most extreme cold and from repeated freezing and thawing. My plants freeze once and thaw once. They don't reach the -10F they'd see outside the leaves, but they must get pretty cold. One year we never went below 8F and the phylodia and pitchers sticking above the leaf pile stayed green the whole winter. They're tough plants.