You are right in making a separate model for the VC.  I don't recall which program you're using, but the principle is the same.

Basically, your VC should consist of those parts that are visible from the cockpit - for example, in a typcial modern airliner, you would include the wings, podded engines, fuselage inside... but not those parts you would NOT see - landing gear, rear fuselage, empennage, etc, then you could go further and delete the polygons you wouldn't see - undersides of wings "opposite" sides of nacelles, etc.

In gmax, you would take these and group them as in an "interior" group.  In FSDS2, you copy and paste into a new model "page"...


As to a multi-res model, your "closer" models may be your basic model with small parts removed, including landing gear, etc., and the "farther" away you go, the models can be basic primitives - enough to give the basic shape.

For example, if I were building a new Grumman Gulfstream I, I would probably use an existing afx source file as the base for an LOD - I get the basic shape, but I don't need the details...  Your lowest resolution model can be as simple as two triangles ..

Basically, use a combination of "removing parts" and quick and simple new models.

Hope this helps

With FSDS2 VC I pretty well finish the external model before i start on the VC.
1) To start the VC, click on Model in the menu
2) From the drop down menu, select ADD MODEL
3) Name the model as VC and check the box that says "Virtual Cockpit"
4) Then (providing you have saved all your parts from the external model) what you do is add the parts to the VC model in order and only add the parts that you think will be visible from the cockpit.
5) As a tip, i would keep the number of parts to a minimum to help with frame rates.
6) For any VC that i make, i have only the internal fuselage structures showing (inc all levers, Yokes & pedals), i face the window polys inwards and cut down the fuselage structure so that only bits (such as the top of the nose cowling) that you'd expect to see are visible.