camping-tents/ is better as it is more user friendly. Non-technical users who don't know what .php stands for will find it easier to remember.
Plus it allows you to use rewrite rules to create a pretend directory structure which is also good for usability. For example if I was a customer looking at camping-tents/gear then without much thought I'd come to the conclusiong that If I just backspaced a bit to camping-tents I could see all info related to camping-tents not just 'gear'.