Forget about traps unless your sniper is actually a crossbowman. Dump dex, will and int, go for full 10 agility, blitz and high as posibble perception. You'll also need a secondary weapon with no range penalty. Naturally a fast assault riffle is the best choice, paired with burst related feats:
It's tempting to go for the gun nut feat but now that it was nerfed instead of made more attractive, it's almost never worth it to sacrifice other stats in order to have 7 int it requires. Doctor feat can be replaced by somthing else like conditioning (you'd have to trade 1 perception for 1 extra endurance though) but I find doctor more useful on hard because of limited healing.