I hope you can get that one to work. A metal tank is a better choice.
Everytime I see a tank mounted on the front of a bike it bothers me. What do you think will happen if you run into something? At least with a metal tank there is a better chance it won't leak even if it gets bashed up a bit.
I don't think a plastic tank in a leather bag would hold up as well.
If it were me I would try to find another spot for it all-together.
User kcmcf told us about this accident
here See how the light on his handlebars is messed up?