chassis year 2003; rv/coach 2006

I rang a local ford dealer and apparently it costs less than $7 in parts for a new spark plug... labour not included.

see link an example of confusion about 5.4 plugs. You have to make sure you get right spec's for your year model. To include torque amount. Plugs are not that big of thing just wanted for you to know about the problems with them. Shouldn't be a deal killer. http://www.f150online.com/forums/v8-engines/415975-2003-5-4-spark-plug-change.html

History: Ford plugs in their Triton motor for whatever reason and 4 years prior to 2003 had a problem with plugs blowing out of hole in the head because they only had 3 or 4 threads in the head to hold the plug in. By year 2003 they added more threads to prevent plugs from blowing out. And when a plug blew out it took the threads with it sometimes. So in (I believe 2004) Ford had one of their even better ideas and installed a 2 piece plug. Sounded great except when those were changed sometimes one of the pieces broke off and a part of plug was left stuck in head. So Ford comes out with a tool that fishes out broken piece, so a simple plug change didn't require pulling the head in case the plug broke while changing. Sort of cutting to the chase, but that is the deal in a nut shell. Now Fast forward when I got mine. 2009 decided to change fluids and plugs. That is when I found out you have to now exactly what you have and exact spec's. I got all kinds of answers that conflicted with what I was reading. I got plugs (motorcraft) from retail auto store. They don't cost much and changing plugs are not that big of deal. Only thing extra I had to buy was an elbow for right side two rear holes as there is not a lot of room. Reading above link should give you an idea of how confusing a simple spark plug change could be. 1 piece or 2 piece, anti seize or not, 2 valve or 3 valve etc... Your 2003 if like mine is 1 piece plug. Just not easy to change with all the stuff in the way.