Well all done, finally - took a bit longer than expected as most things do, mostly due to other commitments. Mudguard connection is a bit Heath Robinson but works. Fair to say there isn't that much left of the original trailer..
Boat sits well on the two bunks and, as Chipko said, once the floor is in the underside is solid as a rock so no real concerns there. Still need to cover the front support with something - didn't get enough carpet to do all three. So far, boat seems to be easy on/off solo, just lift and push until wheels hit the ground then becomes even easier. Boat cover from Ducksback is a near perfect fit (3.5m inflateable model) and definitely worth the outlay, which frankly isn't much more than a quality tarp. The heat reflecting properties seem excellent as well, with the boat more or less cool inside even when sitting in bright sun.
Now to get it wet - with any luck a quick session over the next few days now this persistent wind is finally dropping out..