The Watertown Planning Board heard a proposal to allow prefabricated homes to be stored on Pleasant Street, across from Russo’s market, for about four months. The proposal, presented by Scott Oran of Austin Street Partners last week, would be for 527 Pleasant St., an unused lot that had been part of the parking area for Raytheon. Up to 25 modular homes built in Canada would be stored on the site until they are installed. Each home is 12 feet x 63 feet x 11 feet. The proposed timeline for the storage would be from September to December 2018.