A high quality sleeping bag will do wonders. I have a Rab Expedition 1400 -40 degree sleeping bag. Get one of these and you won’t need a heated tent and you can survive anything. Best equipment investment I have ever made.
My IA just replaced my seat rails using McFarlane seat rails. The rails were good quality and they fit well. He secured them usings rivets as he recommended.
On another note I always use a seat stop...