With rents rising at mobile home parks across the U.S., housing advocates are urging state legislatures to pass bills that would help residents buy their parks if they’re put up for sale. In recent years, large investment firms have been buying mobile home parks across the country, often selling them for redevelopment or raising rent and displacing residents — many of them seniors and people with disabilities living on fixed incomes. Advocates say that offering residents the chance to buy their parks would help preserve a key affordable housing option, while opponents say such rules would place undue burdens on landlords. The debate comes as the nation grapples with a critical shortage of affordable housing.