I've never been in the Cloud Peaks, but cold is cold no matter where you are.
I would plan on temps below freezing in June. I have to believe night time temps in the mid 20's would not be unusual at altitude in that area.
Sleep comfort and cold tolerance is a very personal thing.
I'm not a big fan of space blankets used that way. One issue could be condensation since I doubt they breathe well.
One underneath your mattress may help some.
Instead, I would spend the money on a good, light weight, inflatable air mattress. Some are inflatables are insulated albeit heavier.
I believe it's important in cold weather that getting yourself well off the ground will help you stay warmer.
I sleep wearing long underwear with a fleece hat or a fleece balaclava if really cold. I sleep with wool socks as well.
Just doing that helps me a lot staying warm.
You might also want to carry a set of light weight wool blend or fleece long underwear(top and bottom) to sleep in.
The one thing you want to avoid is
over dressing and then getting sweated up in your bag.
pete