There isn't a F450 car carrier on the road that doesn't have a stretched frame. There is no worry in doing so as far as trucks are concerned.
That's good to know. I've been threatening to get a sit in sleeper to pop in behind my crew cab and stretch the frame, but so far Wife.gov has vetoed the idea. With one of those the young.uns could take turns napping on long runs and I could have a nice little nap spot for solo runs.