HI guys im been modelling one of the truck for my game but the problem is i dont know how would i do the interior.Should i weld it with the hull but then the problem is complex uv map so i really dont know what should i do?
It has 1254 Verts.
Unless you need the interior for some reason, make windows that you can’t see through.
I need the interior because this vehicle need to be enterable.
enterable as first person or third person?
You need to gauge the level of detail you need in particular areas and build accordingly. if you’re doing first person then you can make it a separate object with its own texture for greater detail, third person control would not require as much of a quality texture and you could probably get away with a single map for the whole thing.
Its a third person.OK thanks for that just one more thing how would i close the mesh of the truck because underneath is a hole is there any special way or just connect faces and then just shape it .
there are many different techniques to use, all of which are typically fine and a matter of personal choice.
I would probably just extrude the edges and flatten them to the center and weld unnecessary faces and errors from the extrusion.
So the bottom doesnt needs to have a 100% clean mesh.
Will you ever see the bottom?
IN 99,9% of cases wont 
Yeah i agree with Zerobounds and I would go with the separate object with one texture map =]