fuel tank trunk mat

[cuda hunter]

I have removed my fuel tank due to the holes I received in the original tank on the way to Carlisle.
The previous builder caulked or seam sealed the gas tank trunk mat to the top of the fuel tank. 
Is there a reason for this?  Is this common?  Should I do that to my new tank? 

I don't think so, but I have to ask.

I assumed that I could reuse the mat that was on the original tank,  but as cars tend to do to me it threw me a curve ball. Ordered the part from Roseville.  28 bucks and hopefully not backordered.   

[anlauto]

I just use a bit of weather-strip adhesive..

[cuda hunter]

Did the factory do this? 
Is there a reason why this is done? I would assume the mat would be sandwiched between the trunk and tank therefore not moving around much. And the mat is textured to match the tank in some ways.  Less movement. 

[anlauto]

Yes they are definitely glued on at the factory