Fabrun, nice work. I've drawn the chassis up a few times in a couple of different ways, but never had the time to finish any of them!
I've used Simulation (was COSMOS) loads as I have to use it at work. The main problem I have is knowing what to put into the FEA and then working out what its telling you. All you can really do is put in a known load and compare different designs for stiffness/strength.
I'd love to known how you got your springs to look so good. I hate drawing springs!