Here's how to do the gay character: Have the main young white guy (Matthew Scott) be gay. He's the one we'll all think of as the "lead character" who is "not allowed" to be gay.
And then make no big deal out of it. It's not like sex is going to be the top of anyone's minds, considering that they are trying to survive. A more mature show could delve into some of the issues of these people all being crammed together indefinitely, but maybe they should just leave that alone.
Maybe they'll have an hour of just gay sex at one point. It'd be better than the last season of Atlantis, at least and it'd probably improve the ratings for that episode. Could be interesting.