Strategies for Large Assembly Modelling

I am involved in designing a complete vehicle which will havenumerous components such as structure, cab, walkways, conveyors,crawler tracks, engine, hydraulics, electrics.
There will be a top assembly model that contains everything.
Many of the subsystems such as the cab can be designed as aseparate model and inserted in the top assembly with only a fewmates. The hydraulics group links many of the other groups togetherand needs to run all over the structure, and it seems that it mustbe designed in the top assembly model. I expect from experiencethat working in this model will be slow and best avoided.
Are there any strategies whereby the hydraulics could be designedon a model with only some of the main assembly components and thenappear in the main assembly without duplicating the components.

For example have a model with the hydraulic lines and the structureto work on and then in the main assembly, which already has thesturcture, the structure does not appear twice.

Any sugestions would be appreciated.SolidworksAssemblies