Well a WP4 is 300kgs and with engine and a little kit it will be 400.
A trailer will be over 130kgs, braked more like 175kgs.
So which ever option you go for, braked will be your only option.
My boat is 300kgs empty, with engine (90kgs) and 2 anchors, chain, 150m rope, battery, 37 litres of fuel, etc and 180kg trailer it was (830kg) and over the 750kg unbraked legal towing limit. I have upgraded the trailer to braked and that has added a few 10's of kilos.
So please bare in mind how much a "light boat" can weigh with your gear in it!
(The trailer manufacturer didn't know how much the trailer weighed and it was 30kg more than they expected!)
Rob