THE PLT HAD SUSPECTED A HYDRAULIC PROBLEM PRIOR TO DEPARTURE WHEN HYDRAULIC FLUID WAS FOUND ON THE HANGAR FLOOR. THE ACFT WAS FLOWN TO A NEARBY ARPT FOR REPAIRS. THE ACFT THEN DEPARTED AND APRX 1 HR INTO THE FLT A HEATER PROBLEM WAS EXPERIENCED. THE PLT CORRECTED THIS PROBLEM AND THE FLT CONTINUED AT 11,000 FT. THE PLT REQUESTED A LOWER ALT UPON NEARING MOBILE AND ATC APPROVAL WAS RECEIVED TO DESCEND IN STAGES. AT 2,000 FT, THE PLT REPORTED A FAILURE OF BOTH ENGINES. REMEDIAL ACTION WAS ATTEMPTED, HOWEVER, PWR WAS NOT RESTORED. THE ACFT WAS SUBSTANTIALLY DAMAGED DURING THE GEAR UP FORCED LANDING WHICH FOLLOWED. DURING WRECKAGE RECOVERY, 49 GALLONS OF FUEL WERE DRAINED FROM THE RIGHT FUEL TANK AND THE LEFT TANK WAS FOUND EMPTY. A TEST PROP WAS INSTALLED, FUEL WAS ADDED AND BOTH ENGINES WERE STARTED. THE ENGINES PERFORMED WITHOUT INCIDENT.