How to persuade dogs to potty in new kennel?

Both my dogs have lived with me for several years and have always been great about pottying in their outdoor kennel or their big outdoor pen. They don't go in the house, thank goodness. Three years ago, we moved in with family and they adapted to their new potty spot quickly. We just moved into a new cabin on the family property and I put in a small outdoor kennel for them off the back door (as getting outdoors Dec.-Feb. can be nearly impossible where we live). Since this is new construction, per the suggestion of my builder, I laid patio block inside the new kennel to keep from getting mud everywhere. Neither dog will go potty in the new kennel. I tried pulling up some of the patio block thinking that if they could get on the dirt, they would go potty. That hasn't been successful either. To make matters worse, they can see their old kennel from our cabin (as we can't take it down til the ground unfreezes). I do not take them to their old kennel at all as I want that habit to fade. I do take them to their big pen at least 3 times a day, in addition to our walks and outdoor play time, since they won't potty in the new kennel. But, we are having a lot of ice-over the last couple days and we will soon be stuck at the cabin. They have both gone once in it when they couldn't hold it and I praised and praised and praised them for doing so. Still, they each came back in the house with their heads lowered as if they were ashamed. They haven't gone potty out there since. Does anyone have any ideas of how to encourage my dogs to potty in the new kennel?