Andy, thanks for that idea - I didn't think of using the bathroom scales!! - will be able to give that a go tomorrow.
I've been using the thing as is on the local roads for the past 2 years without a problem - just on the local roads you don't get to too fast cos they're not very straight
My main concern was leaving a full tank of fuel in the boat for the motorway journey which is maybe not a concern judging by Richard's comments - I'll now need to check with the folks in Hull to check that they're happy with the full tank idea
I've got a new axle unit which I will be fitting tomorrow or Monday provided I can find a way of lifting the rib off the trailer without damaging the tubes - may try a couple of scafolding poles with the loadall or something see what happens kind of thing. Once this is fitted, the bearings won't be immersed in water until it's back in Pembs.