Im building one to but in those locations I was going to use a Mica capacitor. I'm not shure which is better for this circuit though but i'm sure either will work!
I'm going for Wima polyester caps. I have seen many pictures of the aleph P 1.7 on internet, and most of them have polyestercaps, and it is no problem to change the caps later.
Im building one to but in those locations I was going to use a Mica capacitor. You can choose any linux SOM caps and a compatible carrier board, to create one that is tuned to your needs.