I went in 2008 and 2009. Camping is the easiest option.
The hotels nearby are usually rented out completely by teams and the others will cost you quite a bit!
The ferry is easy and from London it wont take too long.
It’s easy to get there just be careful not to get lost in Liege like we did!
I’d advise going on the Thursday for the pit walk, always good banter in the Belgium pits :P
If you’ve got any specific questions just ask!