In the absence of any charter provision or bylaw to the contrary, the terms of a policy issued by any company organized or operating under section 6804 shall be construed to cover any loss or damage by fire or lightning to any insured farm vehicle and its contents while located in any building not insurable by said company, provided said property shall have been absent from the insured owners’ premises not more than 10 days and continuously in said uninsurable building not more than 48 hours.