I melted a PCH cpu in my RV's 20"x10" media Cabinet one summer... Comments like it's doesn't need one really depend on the environment you are running it in.
If you intend on taking your 500X2 to Burning Man this year, Aluminum Stick-ON Heat sink's are pretty cheap.
Please inform us more on what size and where to buy, as I am sure a heatsink will be best if fitted an internal hard drive and using it frequently.
My 500X2 is hot as hell and I am only doing copy on HDD at the time (for about 36 hours on a row) as I am filling up the drive with my stacked video's to release my pc hard-drive.