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2 bunks is just fine for a RIB with no need for tube support. The bunks should extend just past the transom, and they will conform to the hull with time and adjustments.
I towed a 14' (4.2m) Zodiac Futura MKII Sport GT with a 40hp two stroke on a steel Pacific brand trailer behind a Gen 2 Prius without any issues. The Prius had a few mods with excellent upgraded wheels and tires for grip <Most important on any vehicle. The boat weighed about 500lbs and the trailer weighed around 200lbs. A RIB will weigh more than a SIB.
Budget is probably important, but an aluminum trailer would be preferable and an aluminum hull is even better. There are a lot of other boat brands out there other than Zodiac. AB Lammina series are very light RIB's. https://www.abinflatables.com/ribs-d...lammina-15-al/
Highfield builds awesome boats but they are heavier, fancier, and more expensive. https://www.highfieldboats.com/classic-360/
There are lots of other brands too, like Honwave's that are very popular.
Lots of things to think about, like do you want a steering wheel or tiller steered? Seating inside the tubes? Hypalon vs PVC for which there will be a large cost difference. What size outboard? How much seating? Launching wheels used for beach launching? Ask lots of questions as there is a ton of experience on this board. You can also use the search function to help answer questions.
"Bigger is better".