Stripping Your Nif
To start with you'll need the original wagon Nif.
Open the CK and in <Activators> find "CartPassenger"
Right-click and <Edit>.
And find the Nif name in the <Model> text-box.
Now you have the name, export the .nif from the game's bsa into your <Meshes> folder and open it with NifScope.
Click on a chunk of the wagon to be removed and you'll see it's branch in the object tree becomes high-lighted.
Right-click the high-lighted branch and click <Block>/<Remove Branch>.
Hey-presto, that chunk has disappeared!
Repeat until you have cleared all but the wheels, front axle & stays.
Now save your stripped wagon with a unique name and it's ready for importing back into the CK.
Download - StrippedCart01.nif
Next, Caravans Part 2 - Undercarriage.