Bringing back this old underrated thread. I am also interested in this and would appreciate any info on how to make one, what material, how to fasten it etc. I am not looking to do a complete flat bottom undertray, just a splitter similar to what Richo did here http://www.sau.com.au/forums/topic/428535-richos-r33-gtst/page-6
Would I need any drawing/design software or is it something that can be drawn/mocked up and cut at home with grinder etc?
Let me know what you all think
Cheers
Amir