I'd suggest measuring the Net Promoter Score (NPS) (link). It's used in business as a better measure of customer satisfaction than more traditional measures. See here for evidence, sorry for the not-free link.

1. "On a scale of 0-10, how likely would you be to recommend the minicamp to a friend or colleague?"
2. "What is the most important reason for your recommendation?

To interpret, split the responses into 3 groups:

• 9-10: Promoter - people who will be active advocates.
• 7-8: Passive - people who are generally positive, but aren't going to do anything about it.
• 0-6: Detractor - people who are lukewarm (which will turn others off) or will actively advocate against you

NPS = [% who are Promoters] - [% who are Detractors]. Good vs. bad NPS varies by context, but +20-30% is generally very good. The followup question is a good way to identify key strengths and high priority areas to improve.