Fergal
Personally I know of no 'practical' courses. All I've ever heard about are bums on seats to pass the exam. When you do it for the first time, that really doesn't give you any experience as such so when you are out on site installing it can be a bit daunting.
FWIW, in your shoes I'd be inclined to see if manufacturers offer courses and go on those. The likes of OSO, Megaflo etc. If you can, then you will learn about application and what they like to see as best practise which in turn will inform your own installation best practise.
Otherwise, it's a case of trying to work with people who do it on a regular basis to learn all the stuff you need to understand that is completely omitted from the examination process.