We have a 2016 and it is not very well insulated. One improvement we did just last week in preparation for the heat is to buy some bubble-wrap-like insuation from Lowe’s (Home Depot did not have it). It comes in 2′ x 25′ rolls. It is all silver. I simply cut 6′ sections and slipped it behind the curtains (it fit perfectly: one for the left, one for the right of both the front and back.) It makes a noticeable difference.
When I want to open the curtains, I simply roll up the insulation that would normally cover the part of the window that we want to expose and clip the roll to the curtains. It looks like a shutter. Hardly noticeable. It took me less than 30 minutes to install with just scissors.
The product is called Reflectix. It is a reflective bubble standard edge insulation. Model: BP24025 Here is the Amazon link: