i will be building a new trailer in the next month or two , it will be a ramp ova type and light as possible for my light suzuki . It will be fully galvanized as I want to be able to wash the truck down on it , much easyier to get under it . So the deck will be bits so spaced channel etc .
I built a tandem axle braked trailer about 6 years ago and and made a center pivot as Reece talks about . Trailer rides well and takes speed bumps much better . I only braked the front axle and had no problems , alas only have about 1300-1500kg on it . I got four falcon front hubs , xf , for $150 from a wrecker including brakes etc . Took them to the general engineering shop and they welded them to some 50mm box for axles for another $150 , so two braked axles for $300

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Something else I learn was when you mount your springs etc mount them on a channel or angle that you bolt to the trailer frame , then you can move it to set a good balance with a load on it .
I welded my straight to the chassis and had the wheel middle 10mm back from the trailer middle

. with the drawbar weight its heavy on the front and with a zuk on there its 125 kgs on the coupling . Way over the limits for most japa 4x4's but luckly well under the limit of my rangie and witrh that tounge weight tows like a dream .
I got a braked coupling , jockey wheel and 1000kg galv springs for under $250 from the guy on trade me . Hmm it seems to be all trojan stuff too . The springs are one piece , so no rust between springs , all for my washdown on trailer thing .
Chris