Also another tip from John Howell "If you have slotted gunnals then you can use the slots at the stern to locate a simple numberplate bracket which sits over the stern post. Holding the numberplate behind the boat."
and from Martin Hughes "Hi Alan I've used a system that slots into the aft thole pin holes,basically a pair of extra long pins that ca board can be attatched to ?
All New trailers must be type approved and type approval deals with light board fittings i.e light board being attached to the trailer. Type approval is all to do with stopping home made trailers that are not safe etc. I would check with your insurance company about affixing the light board to the skiff as to do so may invalidate your insurance.
If you would like to send me your email I will send you a photo of a simple bracket used by us here at Allaboard Bristol to carry the light board succesfully when we towed our skiff to the Fete du Golfe at the Morbihan last year. It goes over a cover or a bare boat and is used on my Whilly Boat as well. John Read firstname.lastname@example.org