[pct-l] US tourist visa to thru hike

[Dave and Cindy]

We have a friend in Spain that will be thru hiking next year.  He is asking for advise on what is the best way to insure a tourist visa from the US Embassy. The embassy is telling him that a letter explaining his purpose of visiting the US would be helpful.  A document with hotel reservations or other accommodations is an example of what they are looking for.  He is afraid that they will not understand if he writes that he will be walking across the country!!!
He will be staying with us for a few days before we all leave to thru hike together.  A letter from us stating his stay with us could be an example of what the embassy is looking for
What have others done in the past?  Is there something that would be helpful from the PCTA?  I will call them on Monday to see what advise they might have but I also would like to hear what others from different countries are doing or have done in the past when acquiring a US tourist visa for six months to hike the trail.
Thanks,
Zelda