On our 2016 31DS we had same issue.
Got some sound and heat reducing sheets from Amazon.
covered the whole inside of dog house and checked both temps
and sound with meter.
Some improvement.
Laid another layer on with triple layer on passenger side.
Big improvement
The sheets are 12X12 and easy to form and cut.
I bought a off brand which is foil on one side and thick sticky dense material
I also have a one piece carpet on the cab floor which I lined
underside with same material.
Big Improvement in Temps and volume.
Passenger and driver much happier now.