Hi lyslexic,
at Sentinel Car Park they should allow you to go alone (as far as I am aware). You shouldn't have security problems with the Basotho as long as you don't sleep over. As far as safety goes, do take proper gear with, meaning a proper weather-proof jacket, and warm clothes, extra food and a space blanket in case you get injured or lost and need to sleep over. Bear in mind that lives have lost in that area due to cold / weather related problems. Please don't join the ranks of ignorant visitors that head up there simply with shorts, T-shirt and a water bottle. Take a cell phone along (generally good signal up there), and save some of the rescue numbers which should be posted on the wall in the office where you sign the register. Get the cell phone number of the gaurd on duty too. Fill in the rescue register properly. Also, don't depend just on the register, check in with a family member or friend when you leave, and again when you are back down (they should be aware of what time you expect to be down).
Have fun, hike safe, and let us know how it went.