As a travel expert dedicated to providing practical guides based only on real, verifiable data, I must point out a critical issue with the request.

“Moss” is a common name for a group of non-vascular plants, not a geographical location, city, or country suitable for backpacking. Therefore, there is no verifiable data regarding summer weather, typical costs, specific attractions, or crowds for a travel destination named “moss.”

To adhere strictly to the “CRITICAL: Only use real, verifiable data” instruction, I cannot create a backpacking guide for a non-existent travel destination. Generating statistics, prices, or facts for “moss” would involve making up information, which is explicitly forbidden by your prompt.

If you intended to refer to a specific, real-world location (e.g., a town, region, or park that might have moss), please provide the correct name, and I would be happy to create a guide using verifiable information.