First question is (always) are you 100% straight ... I don't even know how any straight guy could maintain wood if another dude's leg (or anything) touched any part of you, let alone shit like DP or (especially) DVP
I've never ever had the slightest arousal from any form of the male body, not in person, not watching vids, not ever. Had plenty of oportunity to fuck some seriously hot dues over the years, and have never been even the slightest bit interested in trying even just to see. Same goes for trannies and ladyboys. They're dudes, period. And I'm not interested. Count me among the 100% straight.
So in answer to your question, here's some insight. One of the keys to success of a gangbang is knowing how to navigate the spaces and angles. (There's a pic on fet of me DPing a well reviewed here woman posted by her, and none of my body is in contact with the other dude's. And that was in the heat of the action.) Another key is not losing wood from incidental contact. I think of it like brushing up against a car or sofa, focus intensely only on the woman, and it's no problem for me in the heat of the moment.
I've never done and won't ever do DVP for exactly your reasoning though. They'd have to pay me a LOT more than the Legal Porno dudes get. And even then, no.
I do think porn of a tranny fucking a hot girl is pretty hot, like lesbians except also she gets fucked by a real cock.