You are correct. It is easily fixed. Even a metal bottle would be vastly superior to a plastic one since it wouldn't be so inclined to spray fuel everywhere in an accident. Something like this might work,
Brunton Fuel bottles
Naturally the best place for a tank is on the back.
It is one thing to build a custom bike and then ride it yourself. Things change a bit when you start to sell your creations to others. As builders we have a responsibility to make things reasonably safe.