Phzzzzzzz!
Dannyboy1. In your first post you said you wanted a challenge, you should have bought a Challenger!
As I keep being told to be nice and helpful to people with tigers (Ido have two) In answer to your question about etch primer. I get a large can from Halfords, it will do two or three tank, and work on both metal and plastic. Painting the inside is not necessary. It your choice though. Authentically you could paint it off white before you install any thing.
