In reply to JH74:
Not that helpful as only done the eastern end of it myself (no trailer), but know of various friends who have done the full length albeit without trailers.
The only negative comments of the route were from a couple on a tandem who found it hard work - more due to the tightness of bends and restricted width generally but particularly on corners like when going under the numerous bridges iirc.
At the eastern end parts of the route are very popular with bikes, runners, walkers and dog walkers. Meeting others coming the other way particularly on some sharp blind bends would need care.
Been a few years now, but the Eastern end, was mostly all hard tarmac or gravel easy surface, so should be doable with care on the corners/width restrictions, and by passing some steps! A torch for the tunnel would be helpful though not essential. Much beyond Falkirk I have no personal experience.
Another thing, I recall comments of restrictions and/or inability to book bikes on certain trains (a trailer may be an added problem on busy services?), so suggest you check that out.