TS, have looked at any of the racks that pivot and lift the bikes onto the roof? I think Draftmaster is one of the brands. Maillotpois has one for her tandem. We need to replace our tandem rack so I'll be doing some research. If I see anything, I'll let you know. Let me know if you find something also!
On the trailer, I think it would be fine. I've seen them. But two things, light trailers tend to bounce around a lot so one bike could mean the thing is jouncing all over the place.
Also, trailers are a pain in the patootie a lot of times - parking, turning around, etc. We haul trailers a lot. It takes planning and we try not to unless except for the times we absolutely can't do it any other way (like hauling drift boats or 10 bikes).
Frends know gud humors when dey is hear it. ~ Da Crockydiles of ZZE.