I purchased my G VPP and doing the same with the 370 as well, both preorder. Very simple process. Print your claim form and take it to the dealership, you drop a deposit and they order the car. What I have had both dealers do is find a similar optioned vehicle via search and use that vehicles vin for prepricing purposes just to give me a ball park since the true vin of the preorder car is not yet known. When the vehicle arrives you close on the deal as you normally would. In all honesty on some vehicles you can do better than VPP but on new releases it eliminates all of the negotiation as it is a prenegotiated price. And, since I really hate the going back and forth aspect of this process it really works for me. Not the very best deal but a better deal than anyone can get with no negotiation right off the street. Review all aspects of the VPP website and it should answer all of your questions. Make sure you click on business associates at the top and the incentives login/password is "vendor" for both. Happy shopping.
Here is what the final numbers sheet looks like for a fully loaded 6MT touring will all available options.