If you are going to export the model later in development using the old traditional group-export method, then follow these tips:
1. Do not group objects within a group. This can confuse makemdl and can cause strange effects such as the model being blown out of proportions.
2. All animated objects can only be linked in a single heirarchy using a based object as the parent object. There should be no branching the heirarchy for animated parts.
Example of an acceptable heirarchy:
I. Landing_gear_top [key animated]
--- A. Landing_gear_bottom [key animated]
------1. Rudder_01 [stock animated]
---------a. C_tire_slow [stock animated]
---------b. C_tire_blurred [stock animated]
An example of an "unacceptable" heirarchy:
I. Landing_gear_top
---A. Landing_gear_bottom
---B. Landing_gear_bottom_01 [key animated]
------1. Rudder_01
Notice that the key animations on the first example don't branch off into other key-animated objects like you see in the second example. Stock animations can be branched off since they are not key-framed and only controlled by their rotational axis.
You should only group the exterior and interior models seperately with absolutely no grouped objects within them.
If you are exporting using the xml-based heirarchy-export method, then you don't need grouping at all. Just link the objects to the main node, but follow the heirarchy rule regarding key-framed objects.
Example:
I. Exterior [a simple object - preferably a primitive box]
--- A. Fuselage
--- B. Wheel_well
--- C. Landing_gear_top
------1. Landing_gear_bottom
--------- a. Rudder_01
------------ i. C_tire_slow
------------ ii. C_tire_blurred
--- D. Landing_gear_top_01
------ 1. <You get the idea>
Also, don't forget to reset the scale of each animated object just prior to exporting by selecting the key-framed object, going to the hierarchy tab and then clicking on the "scale" button.
Please remember that everyone has their own way of getting things to work right. So my method is "not" the only solution.