Then gravel surrounding a perforated pipe of adequate dimensions (size depends on how much water you're dealing with) covered with a filter-fabric sock.

That's putting it delicately! 

You also delicately mention, "...the existing plumbing pipes that exit west of the bathroom."

The fabrication cost is more expensive but I can typically be in the range of 20-25% more than laminate and get a product that is significantly superior in quality and actually adds value. 

The key thing is most banks need to approve the fabricator for container homes, its going to be similar than any other modular home where the bank either has to be cool with a different draw schedule or a the prefabricator (container company) has to be cool getting paid a little bit after they've completed their work.But in most cases where the container company is legitimate, I think one can find options. 

A few examples where the branded products should not be applied include wood or painted surfaces, aluminum products, metal (including stainless steel), faucets, marble, natural stone, and, of course, carpeting, fabrics and paper.

It is the bullnose/edge that is pre-fabricated.  

I see a number of people posting on FB groups that fabric for the headboards is a regret. 

While we had a telehandler on site to move lumber and help frame walls I decided to rent a big crane with an operator to help set the pre-fabricated roof trusses.

I was just pointing out what my 5 ton units cost me installed.As for quartz, I get 1/2 slabs from $300 to $550 depending on color and about $400 or so for fabrication/install.