We did something somewhat similar to this last October and November. We have a KZ 14' Sportsman Classic, with no furnace. We use a Ryobi generator with a electric furnace. I did take the time this last summer after we had purchased this unit. I put the R5 pink stuff, with the Reflectix glued onto the top of that, under all benches, inside of the storage area on outside wall, and Reflectix on the inside of the storage area. Pink stuff inside of the water tank, water heater, shore power area also. No Reflectix there.
Did that make it any warmer? Don't know. This was our first year of fall/winter camping with it.
Will it make a difference for next year? Don't know. I will be insulating it more inside all the cabinets on the outer wall/ceiling, and the closet also. Am thinking of pulling the tub surround at the bottom, and putting in there also.
For you, Have you thought of doing something similar to your trailer? A little insulation and elbow grease might be the thing for you. Just make sure that all your measurements are good, and your cuts are tight as well.
Oh, one other thing. The wheel wells/fenders on the inside of the trailer, these I covered first with the Reflectix. That was just sheet metal there!
Hope this will help you somewhat.