public class MyVehicleClass extends VehicleBaseEntity {

    private static final VehicleBuildInfo buildInfo = new VehicleBuildInfo(VehicleClassification.Zepplin)
            .SetEngineCount(2)                                      //example properties
            .SetEngineType(EngineCategories.Aircraft_Propeller)     //this example uses the Zepplin vehicle properties
            .SetMaxEngineRPM(3000)
            .SetMaxSpeedMS(70)
            .SetGasCelCount(8)
            .SetGasCelCapacity(1000);

    public MyVehicleClass(EntityType<?> Type, World WorldIn) {
        //The parameters in this super are the Type, the World, an array of seat positions and the vehicle build info
        //specify as many seat positions as you want in this array as it loads all of them as player seats on the entity
        
        super(Type, WorldIn, new Vector3d[]{new Vector3d(0.0D, -1D, 0.0D)}, buildInfo); // The super class handles everything entity related
        
        //this allows you to completely customise how the camera is structure for the vehicle,
        //the first Vector is position offset, the 2nd vector is rotation, 
        //and then the first float value is 1st person FOV with the 2nd float value being 3rd person FOV
        
        VehicleCameraSettings.AddEntityCameraPreset(this.getType(),
                new VehicleCameraPreset(new Vector3f(0,4.0f, 16.0f),
                new Vector3f(0,0,0),70,65f));
    }
    
    @Override
    public void TickUpdateEvent(){
        //this is called by the super class every tick update 
        //and is a safer way to add code without overriding what happens in the parent class
        //you can still @Override the normal tick update though
    }
}

The entity renderer:

this you put an array of models in but for this example it's an array of 1 size, this is so you can put multiple models for a single vehicle in, or make it dynamically swappable in game

@OnlyIn(Dist.CLIENT)
public class MyVehicleRenderer extends VehicleBaseRenderer {
    public AirboatRenderer(EntityRendererManager renderManagerIn) {
        super(renderManagerIn, new EntityModel<?>[]{new MyVehicleModel()},"textures/entities/MyVehicleTexture.png");
    }
}

Registering the entity

you register the entity as if it were any other entity

    public static DeferredRegister<EntityType<?>> ENTITY_TYPES = DeferredRegister.create(ForgeRegistries.ENTITIES, MOD_ID);

    public static final RegistryObject<EntityType<MyVehicleClass>> MY_VEHICLE =
            ENTITY_TYPES.register("my_vehicle", ()-> EntityType.Builder.create(MyVehicleClass::new,
                    EntityClassification.MISC ).size(3f,2f).build(new ResourceLocation(MOD_ID, "my_vehicle").toString()));

Registering the renderer

this is also the same as if it were any other entity, it is put in the client event handler

@Mod.EventBusSubscriber(modid = MOD_ID, bus = Mod.EventBusSubscriber.Bus.MOD, value = Dist.CLIENT)
public class ClientEventHandler {
    @SubscribeEvent
    public static void init(final FMLClientSetupEvent event) {
        RenderingRegistry.registerEntityRenderingHandler(ModEntities.MY_VEHICLE.get(),  MyVehicleRenderer::new);
    }
}