The V-rep model is not automatic to produce. You have to build two models :
_ One for the calcul
_ One for the visualisation
And you also need a special urdf to import the 2 models (have a look at the poppy one).
The model for visualisation can be a bit complex, you just need a powerful computer but the model for calculation have to be very simple and more convex as possible.
Here a thread explaining how to do : [CFC] Reduce 3D meshes complexity of the URDF model
From what I remember I used the convex hull algorithm and sometimes I had to work by part for concave bodies.