The M is just a touch short of 100 dB loss. However you only approach that at 8 kHz, and most of us with a ski slope loss are not going to hear a thing at that frequency anyway, with or without hearing aids.
I had impressions done at Costco today for molds. I wish I had done it earlier as it is no big deal. Their warranty is excellent. In Canada you have 3 months to return them for a full refund, or replaced as many times as necessary to get a good fit. She says they are flexible and will stretch it to 6 months. Suspect warranty is better in the US. With a Select-a-Vent they are pretty flexible to adjust for vent size.