I am trying to create an air bag sub assembly that will auto resize based on changes to the main assembly, and don't know the best way to go about accomplishing this.

Attached are the files I am working with.  Here are the issues I have ran into so far...

1.  I have created the air bag and put dimension limits so when I raise the end up and down in the assembly it changes the air bag to fit within the stroke limits of the air bag specifications.  It all appears to work fine in the asm.sldasm.  However I have to hit update after I move the end up and down.  Is that expected behavior?

2.  Can you look at my assembly and see if how I did the the bag portion part sketch ok?

3.  When I save this assembly it asks about the internal part and saving it separate or as part of the assembly.  What is it asking, and are there any downfalls to saving it internally?

4.  I want to use this assembly in and constrain the top and bottom plates to the parts they will be lifting, and then when I change mates I would like it to auto resize.  Is this a possibility?  I have tried making it flexible, but that doesn't seem to be working.  It won't update the air bag when I click update.