Can we declare a var Stable?

public type Post = {
    pid : Nat32; // Post Id
    uid : Nat32; // Speaker's User Id
    ppid : Nat32; // Parent Post Id
    xid : Nat32; // Xchange Id
    tid : Nat32; // Thread Id
    cid : Nat32; // Conversation Id = Discourse Id = Issue Id = Topic Id, etc.

public type bufferPost = Buffer.Buffer<Post>;
private stable var container : Trie.Trie<Nat32, bufferPost> =  Trie.empty();

Above code is giving me error !
variable container is declared stable but has non-stable type
Trie/176<Nat32/12, bufferPost/78>

So, is this due to Buffer , I am using?
Can’t we declare a Trie stable which is using buffer as its Value?
I am using Buffer to get some optimisation instead of using arrays.
To get rid of above error , only way possible is to use arrays?

This might help you, you don’t need to change the Array, just use the Buffer when using the append method.

Can you help me with this ?