We have a motgage loan on a farm which includes a mobile home, barn and 40 acres. This property is in a flood zone. The repacement cost of the mobile home and barn is $90k according to the appraisal which is 3 years old. The customers insurance company will only write flood for $50k because they say the mobile home has depreciated. What coverage are we required to have.

Is the collateral securing the loan both the mh and the barn? What is the value of the property minus the land?

If Both mh and barn, $90k, then $90k in coverage.

What is the amount of the loan? I think that fits in there, too. It should be the lesser of the two: $90k or amount of all outstanding loans secured by them.
Anyone else have any thoughts?

The lesser of
1)Value of improvements less land
2) loan amount
3) maximum coverage allowed by law