here is a bunch of videos you can watch and get ideas from
you can buy the insulation boards from Homedepot or Lowes
https://www.google.com/search?client...onditioner+mod
Get the proper air conditioner tape... silvery metallic tape that has paper you peel off the sticky part
and while you are at it look for air leaks around slides etc
no use improving air flow if you loose it through poorly fitting panels/windows etc