I've got to say that whilst I can see what you are trying to do, it just doesn't quite work for me. Taking snowtrooper armour and painting it with the shapes seems a little like you are trying to cut some corners. I realise this is not the case and that you are trying something new, but fans won't know that. A better approach would be to have a chestplate with the detail molded in.
The P90 is a good choice but I agree it needs some work before anyone is going to look at it and see a blaster and not "those guns for Stargate SG1". The Asylum's suggestion is good, whilst Toragh's has the excellent advantage of being an actual screen used blaster!
As regards to calling it a Mandalorian Commando, the only flaw there is that regular Mando's are Mandalorian SuperCommando's
Please note that I am not trying to be offensive, cause trouble, start an arguement or the like, but simply to be helpfull and offer my advice and experiance