I have been contemplating which Space Marine chapter to build and I think Red Scorpions is the way to go. Now for fluff and traits. I have a few traits in mind that I think suit their fluff.
1. Honour your wargear. It was said that a large amount of Devastator and Tactical Dreadnought Armour (Terminator Armour) was collected shortly before the powers of chaos attacked their homeworld.
2. Purity Above All. They are constantly monitoring gene mutation because of their gene splicing with the Fire Hawks.
3. Scion of Mars. They had a lot of extra help from the Adeptus Mechanicus compiling their armoury. Although I don't know if this trait would be terribly useful.
4. Trust Your Battle Brothers. They are known for being courageous and don't falter. Counter Attack seems like a fitting ability. (would this be useful on Assault Marines as they do not carry bolters)
This was all based on fluff I read on this website.. http://www.garbled.net/40k/red.scorpion.history.html
If anyone has something more official, or something not mentioned in this website, I am all ears. Thanks all.