I've been trying to trouble shoot a problem with Fedex for two weeks and finally figured out the problem, which I thought I would share with everyone. In the Notes section of the module the documentation isn't clear (or maybe even flat out wrong). With that said, the Fedex documentation isn't too clear either.
 
This issue is for people using Fedex ground and for packaging uses YOURPACKAGING (not using any Fedex boxes). The same issue might apply to other circumstances, but I can only tell you about our specific issue.
 
In both the Fedex and Viart documentation it says that you must include the dimensions of the package in the communication with Fedex (variables in the module). This isn't exactly true. If you're using YOURPACKAGING you can just put "1" under each Width, Height, and Length variables.
 
We use Fedex all the time, using YOURPACKAGING from their web interface, and we never include any dimensions, only weight (you must have weights for your products). Given that, we finally figured out there must be some easy solution.
 
Hope this is some help to people (I asked Viart to change the notes in the Fedex module).

thx!

I got word from Viart that they will make the necessary adjustments in the module notes for the next release.

This is great. I am based in Canada, and I assume your in the US.
Can you please shed more light on shipping.
I have many different products, some can ship in an envelope, some may ship in 1 box, some may ship in 5 boxes. Some may buy 1 product, and some a combination. Only weight is important for each and every product? Not number of pieces? Not dimension of each box?
I use my own packaging for all items.

If you use Canada Post (CPC), you will need to package everything into a single box. In our store we set a weight limit of 10kgs for CPC and no limit for Fedex and UPS.
 
With all carriers your shipments are priced by mass or cube (volumetric equiv). The cube calculations in Canada are l_cm x w_cm x h_cm /6000 = kg. You may need to gross up the weights in your product records to be sure you have the right cubic weight for each product.
 
To make this clearer, a paperweight 10cm x 10 cm x 10 cm weighs 1kg on the scale, and cubes to 0.17kg -- you will be charged for shipping 1kg. A case of potato chips that measures 35x35x40cm and weighs 1kg will be charged at the cubic weight of 8.2kg.
 
It's important to make sure you have multipeice pricing with other carriers, particularly FedEx HD service.