We'll want to sleep at the Portal to help with acclimatization - I think 5000' would be too low. But I'm confused what you mean about no-shows? I thought the backpacker campgrounds at the Portal were first come, first served? I'm just unclear where they are exactly, or the logistics of using them.
What I meant my no-shows is that people reserve the sites via recreation.gov. Sometimes, life has changes and people are unable to make it.
Drive around to each vacant site. There is a placard with names and dates. For example, you see dates for 07-20-14 to 07-26-14. It's 07-23-14. Chances are those people were unable to make it.
Let the camp host know you would like to set up camp and pay your fee.
