or you could rip the orange box's portal rules straight to brikwars. UR of 2, range of 12", and opens up one portal per turn. things go in one end, and out the other, and vice versa. this includes bullets, boxes, bombs, minifigs, and weighted companion cubes. i'd also reccomend using a marker for the portals, but i'd go for the transparent colored round plates to represent em. you know, the 4x4 ones? i know trans blue and trans red are common, but if you had a trans orange one it'd be perfect.