Maya: Gas Pump

This is the Lynda Tutorial set by Robin to model a Gas Pump in Maya and texture it.

Start out by creating a bounding box.

Then add in a square polygon at the centre of the bounding box.

Shape the polygon by adding subdivisions and bevel the edges. Then delete the top faces.

Fill the hole at the top face. Extrude the face and scale inwards slightly. Repeating this process creates a smooth edge.

Add in edge loops to create a square face in the centre of the pump. extrude this face inwards and smooth out the new edge by shifting the vertices.

Smoothed model.

Unwrapping the UV's ready for texturing.

This is the point I have got up too. It is at this point I have got stuck. The tutorial does not explain how to unwrap the entire object or how to 'stack' UV's. The commentator mentions it but doesn't explain how to do it and assumes you have already done this in the next stage. Below is what he says before skipping this stage and moving on to the next tutorial.

 "I'm going to keep unwrapping, and I'll look at unwrapping the sides and the top in the same way, and stacking those shells. Once I've got it unwrapped and flattened and distortion-free, I can lay out those textures to optimize that texture space and start painting in rust."

I watched the next video but this wasn't mentioned. I have tried to unwrap and stack the shells myself but I haven't been able to work this out. Even after looking online for a solution I am still unsure about this.

How do you save the UV's? Do the shells stack automatically? How do you flatten them? How do you lay out those textures?