If the minimum wage worker had free housing, food, electricity, etc. your calculation would make sense. Generally if you are a minimum wage worker who is working full time, a large component of your disposable income goes into those things (living paycheck to paycheck).

So having a disposable income at all is a luxury, even if it's 10% of your income. Assuming that 10% figure, you can multiply those 3 days by 1/10% = 10 and you get 30 days of working for one weekend of camping. Not really great.