Joining interior with exterior question

[sliwka]

Hi folks,
Any idea what should be used between interior and exterior walls?
To fill those craks and gaps.
I discovered that after fridge removal.

[David Tilston]

I'm a big fan of fibreglass. Remove the sealant, sand the two pieces to bare fibreglass and close the gap with fibreglass and resin.

I'm assuming that the picture is of a classic Trillium. I have never seen one that had fibreglass under the fridge. Typically, you would be looking at plywood there. Since the shell of the trailer is what keeps the water out, there really is no problem here.