PR Newswire reports from Tampa, Florida, that with tight credit and higher down payments required for home buyers, the rental market is increasing in factory-built communities across the Sunshine State, driving up their value.  Because of the real estate boom, some communities have been converted to other commercial use, leaving fewer alternatives for rental housing.  Most zoning has forbidden the building of new communities, but many have been grandfathered in and have become more upscale single family neighborhoods.  Andrea Ciuba of Global Commercial Real Estate Services, LLC, which specializes in manufactured housing community sales, says banks are not lending on these properties, but cash buyers are competing for them because return on investment can be in the teens.