Hi,

There was a small gap in the geometry where you booleaned (not sure why unless you have the model before the booleans) + an extra face near the back

If you are using V2 (beta) of MoI then you can use the script to show any naked edges which at least points you in the correct direction.

The script is:-
script:var gd = moi.geometryDatabase; gd.deselectAll(); var breps = gd.getObjects().getBreps(); for ( var i = 0; i < breps.length; ++i ) breps.item(i).getNakedEdges().setProperty( 'selected', true );

I have attached a copy of your model which is now solid.

- Steve

EDIT,

Updated model