I have used both Krown and Rust Check, and I would very much recommend Krown in terms of quality of product, application and price. Krown was cheaper, faster, application was more thorough (even cleaned up my engine bay, made it look brand new!) and I was able to watch them do the deed while I had a coffee. Surface frame rust on an 08 is nothing to worry about, surprised you didn't get any sooner considering you haven't got it sprayed yet, but I would definitely start this year.