Not sure why you think the trailer lighting board is illegal
ah you see I don't think
its illegal-I know its illegal.
The weight on the axle if weighed on the road will be the weight of boat+ equipment + trailer minus the load being taken by the hitch. But on your car that allowable weight will be probably 50kg max at a guess. There will also be a weight limit on each car axle and a max train weight (the max weight of the loaded car and trailer combined). Ok its all mass instead of weight these days but I'm old school!
Still you may be within weights of course but I sorta doubt it and someone else's claims when they were trying to flog a boat isnt a good guide at all and certainly no defence in law. Take it to a public weighbridge and find out eh.
Oh and yes in a long and eventful life I have been there and done that, and as it happens also built a couple of trailers. Bugga to paint every year though.
Going back to the lighting board, some years back a journo from Sea Angler mag was pulled for exactly the same set up.