I would stay with the size fuse the bike calls for. You could burn up the wiring harness. Instead, I would check the fluid in the battery. Lack of fluid will create resistance in the charging process. Always carry a spare fuse. And I believe that the headlight on during a sunny day is a waste. I truly don't think it helps in being seen.
As for the rust in the tank issue, I feel that the liners are a bit of a waste also. If you de-rust the tank(be careful, the chemicals used can harm paint), and keep fuel in it, it should not rust again. Gasoline displaces water, which causes the rust. So, if you ride it at least once a week, the gas will coat the walls enough to keep the rust from happening again. And if you use the reserve regularly, any water that gets in, will be purged into the carb bowls. And that's one of the reasons why there are drains on the carbs. Every 3 or 4 weeks, I get the drain tubes over a cement surface(the best place to drain and not damage an asphalt surface) and open each carb drain for a few seconds.