Salty69,
I had a Kingfisher 630 purchased new on 06, had 150 Honda on her, yes she was heavy as well but towed it up to Omaha a lot and to Tauranga, towed with a Prado and besides being a tad heavy was the best boat that I had and towed on a single axle, that was on a trailer made in Te Puke. I guess mine was heavy as I had 5mm hull and 4mm sides and deck when I ordered her. Best boat I had in NZ.
I believe that they are still made to order in Tauranga but not 100% on that. Used to go out west thru the Manukau bar with ease.
But it was sold in 2012 as I moved to Perth. A friend also had the same boat and he has upgraded to a trailer with duals and you don't even know that it is behind you [he has a Navara]
That may be a thought for you
Regards
DD