It's not hard to clean a gas tank, put sand blast grit in it, take out pet cock tape up hole, wrap tank with towels and bubble wrap put in the dryer for an hour with no heat, comes out nice and shiny...
TBRider, the inside of the tank is spotless, it's the outside I'd be more concerned about. The roughest areas are at the bottom of the tank externally, where the paint is peeling a little due to the ding on the left side of the tank. The rear of the tank appears fine. Thanks for your idea of an inside wash though, we may need to do that yet!