At 6', I've had occasional 'issues' inside trailers.
To be honest - the actual HEADROOM issue never was all that important to me. I didn't really spent all THAT much time standing straight up in the trailer, so it never really bothered me that I was brushing against the roof, or standing with my head kicked over slightly.
On the other hand...
The length of the bed was a serious issue. If a bed is too short for me, it REAL uncomfortable REAL fast.
Mike