We have a loan that will be secured by a home and three outbuildings (basically small to medium sized hunting cabins). The RCV for the entire property (home, garage, swimming pool, and three outbuildings) excluding land is $280,000. The loan amount is $300,000.

We can't tell from the appraisal's RCV how much is attributable to each building. Can we reasonably assume the home is insurable for the maxumum $250,000 and then require $30,000 additional coverage on the three outbuildings?

What is the safest approach to determining adequate coverage on all of the buildings?

The OTS says to use appraisal value, if it is not available then to use the hazard insurance replacement cost. Although they didn't specify mutliple buildings it should still apply in your situation.

"The OTS says to use appraisal value"

I am assuming that you are referring to the "cost approach" and not the "market value" approach.