Reflectix will work to stop heat but be careful with its use. I used Reflectix on the door window to stop heat and morning light. Left it there while the TT was in storage, the next time out the door window fell down about three inches. The supports that hold the window up are made of plastic and they melted.
So my suggestion is to be sure the window can take extra heat the Reflectix will add to any window. Or place the Reflectix on the outside of the window to stop heating the window and trailer up.