It actually goes on very thin and very smooth. It basically is a "skin". Interesting concept, I've used it on small items and the downside is it is not very durable. I'd guess if you hung your ram out the door, and areas of regular contact would scuff and degrade pretty quick.
have seen a number of posts of cars done this way. One clever idea was a guy who had stripped the car to bare metal and had to let it sit for a long time, a few cans of PD and its covered and fairly well protected form the elements until he could get back to it.
May stop by the shop and tell 'em to hold off on that Wimbledon white while I run out and buy some cans of purple PD! :wink: