Use of imparfait

Question

Why is plus-que-parfait used in this text in phrases such as "   Sarah et moi avions loué un camping-car  .."

Accepted Answer

Hi Meryl,
Because you cannot use the imperfect in French for these actions in the past. They all happened while 'she was still living in Brittany', an ongoing action.
The French language is more precise here by using the pluperfect -
We (had) rented a camping-car = nous avions loué un camping-car
not
we were renting a camping-car = nous louions un camping-car 
nous avions voyagé ... = we (had) travelled to ...
not 
nous voyagions= we were travelling 
etc.
The imparfait would indicate a habit, not an action...

Answer

I can see why you wouldn't use the imparfait, but why not the passé composé? nous avons loué? In English "had rented" sounds too far in the past, like something they had already done before the trip started and they then happened to use the camper for their trip?

Answer

So then when the passé composé is actually used (in the last sentence) is that because it's not being contrasted with the imparfait within a sentence?