poly, yes that is indeed what i was suggesting.
i have amended my post to add %...thanks.
The weights i found via google-
Boat bare- 80kg ( i find this hard to believe but the plate on the transom will confirm )
7.5% = 23kg.
round numbers here i'd shoot for 25-30kg and be done with it as the boat is bound to be heavier than the printed numbers.
please note, the above is based on recommended small trailer weight towing in accordance with the caravan club, which google also gave me. I have never towed anything this light but the theory is sound and i'd be happy to start there.