Implementing own 2D-grid-like TreeModel with gtkmm3

[Alexander Tumin <iamtakingiteasy eientei org>]

Hi, i am trying to implement own TreeView model, by deriving from 
TreeModel class.

Currently it looks like this:

--------------------------- 8< -------------------------------
template <class T>
class GridModel
        : public Glib::Object
        , public Gtk::TreeModel
{
public:
    GridModel();
    virtual ~GridModel();

protected:
    /* lots of virtual methods to override and implement */

    std::vector< std::vector<T> > grid; // <-- how to make this better?
};
--------------------------- 8< -------------------------------

But is this good?

Is there a way to get rid of templating model class itself, hide this 
template somehow so implementation will be possible to reside in .cpp 
file instead of dumping everything into header just because of template?

Is there any mechanisms for that in gtkmm3 ?