Geoff is on the money referencing axle and tow ball loads. When I built my trailer which is;
5.5 x 2 x 2 in the shell & 6.7 x 2.3 x 2.3 in its extremities I couldn’t get and clear and accurate information from the experts because a bike hauler, by its nature, will never be loaded and weighted the same time twice over. My trailer takes 6 bikes which on any given day can be between 600 kg and 700 kg. Add another 200+ kilo for fuel, gear and the usual junk that you carry and it not unreasonable to have a payload of 1000 kg’s. For a car trailer this is easy because they distribute the weight over 4 contact points, much like a horse trailer. Caravans are well thought out (usually) and it’s easy to set loading. By the way I have seen so many caravans “converted” to bike transporters and they become an instant pig to tow because they upset the weighted points within the chassis.
I notice that your axles are set back well beyond the centre line which is o/k but the extra area that has been added to the front will mean that weight can be stored in that area which was not originally engineered into the design which will seriously affect the download on the tow ball. I note that you have a Navara which has a 3000 kg braked towing capacity (if it’s a 2.5 STX) with a staggered 300 kg download according to the rear axle capacity so you shouldn’t have to many issues, but if you want to use a Commodore or Falcon, forget it, they simply won’t be able to cope.
For what it’s worth, my advice is;
Engineer your bike mounting points and location of miscellaneous items such as toolboxes, pit tents etc then adjust your axle and ball download points accordingly.
Unless you have a specific need, don’t line the inside of the trailer above the 1200 mm point as it its unnecessary weight in a place that you don’t need it, i.e. making it top heavy.
If the trailer is nothing more than a bike hauler, my experience is that you have little need for sinks, fridges, lounges, etc
Provide for plenty of ventilation as hot muddy bikes in a cold trailer created plenty of condensation.
