Is it possible to leak where strap bolts in bottom tank?

It is not likely that the tank is rusted (this should be a metal tank) through so that it is leaking from under the strap. However, I would just remove them one at a time and make sure. It is more likely that the issue is there is a leak higher up and it is just running down the straps.

I would inspect for fuel lines running over the straps as they are more likely to leak and drip on to the strap and it runs down to the middle of the tank/strap which is the lowest point.

Please take a look at the info below on how to remove the tank and it explains how to remove the strap but it is just one bolt that holds it together. You should be able to loosen it enough to see if there is a hole under the strap. If there is, it should leak more as you loosen it.

Let us know if you have questions on this. Thanks