Attach truck to boattrailer

[LRNSR]

Hi, i need help about how make a car can attach to the boat trailer. Indeed, the bison works perfectly, but if example i use a add-on truck and change in vehicle.meta and add manually lines, something like that:

<trailers>
<Item>boattrailer</Item>
<Item>trailersmall</Item>
</trailers>

it still don't works, and my addon truck will not attach to the truck.

Any idea?

I'm using gta 5 on social club, and i even tried to change this vehicle.meta by bison's one (changing each "bison" by name of my addon) but still don't work.

Thanks for help