Here is a link to all of the main "underliner" links that reference underside and interior applications of similar products. It contains a main link with links to the other two at the end of the thread. It appears that many products are viable for both inside and underside use.
The last post in the main thread has links to the two others:
https://vintage-vans.forumotion.com/t43347-bed-liner-as-undercoating-sound-deadening
Or you can access them here directly:
https://vintage-vans.forumotion.com/t24130-old-undercoating-removal?highlight=undercoating
https://vintage-vans.forumotion.com/t9474-undercoating?highlight=undercoating
The last post in the main thread has links to the two others:
https://vintage-vans.forumotion.com/t43347-bed-liner-as-undercoating-sound-deadening
Or you can access them here directly:
https://vintage-vans.forumotion.com/t24130-old-undercoating-removal?highlight=undercoating
https://vintage-vans.forumotion.com/t9474-undercoating?highlight=undercoating