Here you go.
Obviously it would be necessary to modify it to make it UK road legal (you might want suspension, brakes and lights for starters!) but the basic design of the trailer can be seen in the pictures.
Not at all in the same league as Bedajim's trailer, but what it provides is a very strong trailer (it has been used off road by other owners and will be by the new owner) which supports the boat very well off road and on rough roads - it has full length keel support and the bunks lay flat against the hull so it's about as good as you could get in that respect. It means it needs a steep beach to launch on, but there is such a beach exactly where I launch anyway so it wasn't a major problem once I got used to it. Smaller wheels would have reduced the depth needed - it had 7.50x16 Land Rover tyres fitted. It also had an extending drawbar - the hitch was mounted on snug fitting box section slid up inside the main spine of the trailer and retained with 2 x bolts through horizontal holes. Take those out, and you could pull the drawbar out about 6ft to get the boat further into the water, though I never used it.
It is based on old Land Rover hubs and stub axles welded onto the axle tubes so the wheel bearings are cheap and easy to get and pretty heavy duty as well. I think the spine for the trailer is made out of the leg that holds the roof on the side of a Portakabin, and the towing ring was a NATO 76mm eye off an Army trailer. The centre bunk is covered with old rubber conveyor belt out of a quarry crusher and I think the side bunks were heavy duty ex military fabric fuel hose. Mudguards also made out of conveyor belt.
No Argie howitzers used anywhere to the best of my knowledge