Isn't there a foil that has the reflective on both sides? I just saw some at Home Depot. I was thinking of lining my ceiling in my GN area as well. Mine would be more for keeping the heat from the heater in. I get cold at night and usually have to use my heater. I don't have sissues with the heat during the day since I have the white fiberglass roof. (That makes a huge difference.)The inside of my trailer has an aluminum roof. Classic did this with their trailers. Fiberglass roof on the outside and aluminum sheet underneath on the inside. So, in essence, I have two roofs.

The shiny side out will work quite well, especially if you are located in a hot, sunny climate. The insulation with foil on both sides functions most effectively, if you have temperature extremes, a large LQ and a moderately sized heat source. Unfaced rigid insulation also works well, and has been used successfully in many installations.

I would not undo what you have already constructed. If you have more foam sheets yet to install, you could first replace them with a double foil faced product. Basically you will have the same amount of insulation, but will differ in the amount of reflected energy you will loose or save.

We have a moderately sized LQ, built a decade ago, using only thin fiberglass matting. At below freezing temps, a small disc heater will easily maintain a comfortable inside environment. The "R" values of the foam and glass insulations are quite different, with the foam being much more efficient.

Regardless of which foam product you choose, there would not be enough difference that you won't be able to keep warm or cool. You shouldn't notice difficulties whilst using any, of the varying facings of the rigid foam products.

Make sure to seal the joints with a spray foam and tape. Also cover the inside facings of the wall studs with insulation, before any wall covering is installed.

BOL