Notwithstanding the terms of any motor fuel franchise, the interest of a motor fuel retailer under such an agreement shall be considered personal property and shall devolve on the death of the motor fuel retailer to a designated successor in interest of the retailer, limited to the retailer's spouse, adult child, or adult stepchild or, if no successor in interest is designated, to the retailer's spouse, if any. The designation shall be made, witnessed in writing by at least two persons, and delivered to the motor fuel refiner-supplier during the term of the franchise. The designation may be revised at any time by the motor fuel retailer and shall be substantially in the following form:

"I (motor fuel retailer name) at the . . . . . . service station located at . . . . . ., in the City of . . . . . ., Washington, designate . . . . . . as my successor in interest under RCW 19.120.030 and . . . . . . as my alternate successor if the originally designated successor is unable or unwilling so to act.

I so specify this . . . . day of . . . . . ., (year) . . . ."

The motor fuel refiner-supplier shall assist the designated successor in interest temporarily in the day-to-day operation of the service station to insure continued operation of the service station.