Plumbers....adding a shower drain questions

Keep in mind that in winter, without a shower-trap,It is possible for the closest vent stack to pull your nice warm moist bathroom air right up the stack like a chimney-pipe, to eventually freeze when it hits atmosphere. Guess what will become your new vent .... And every toilet in the house higher than the shower will force a little air now trapped in the pipe, to vent out that shower-drain,lol, cuz the water cannot come down as a slug, unless the air ahead of it has somewhere to go. As the slug passes the shower,it ain't gonna pull a vacuum on your frozen stack (s). So there is your floordrain, exhaling noxious fumes, then inhaling your warm air.I mean it could happen... am I wrong?
It has to have a trap, and you already know that. But IMO, it also has to be accessible for clean-outs, cuz you really don't want to send that hairy soap clog out the main line. It it hits something in there it can't get past, you'll be calling the Roto-Rooter man.
But, I suppose the trap doesn't exactly need to be right there under the floor. You could put it in a box somewhere more convenient.