I agree with what Turbs said.
You can buy a unit that only protects against Spikes (and they still call those surge protectors), and that's the part of any protector that is rated in Joules...
but it's not really anywhere near what you need for "Surge Protection" on an RV. Good surge protectors, like the one you were referred to above, also protect you against mis-wiring in the pedestal and against over-voltage and under-voltage situations. They do that by not turning the power in to your RV. In addition, you can also buy something called a voltage booster that will increase the voltage in low-voltage situations (rather than just leaving you without power). The latter are heavy and even more expensive.
There are many threads on this forum on this subject so you might search if you want more information.
Edit: Here's a comparison chart showing you some different options: http://www.rvupgradestore.com/Articles.asp?ID=279
And here's another thread with lots of information.
Surge Protection-Those that have one-what did you buy etc