DURING A WX BRIEFING, THE NON-INSTRUMENT RATED PLT WAS TOLD TO EXPECT NO SIGNIFICANT EN ROUTE WX, BUT WAS ADVISED OF LOWER CEILINGS ALONG THE COASTLINE, LATER THAT NIGHT. THERE WERE NO RECORDS OF EN ROUTE WX BRIEFINGS. WHEN THE ACFT WAS ABOUT 40 MI NORTHWEST OF THE DESTINATION, THE PLT CONTACTED CORPUS CHRISTI APCH CONTROL & WAS ADVISED OF IFR WX IN THE VICINITY. HE REQUESTED & WAS PROVIDED RADAR VECTORS TO HIS DESTINATION, BUT WAS UNSUCCESSFUL IN FINDING THE ARPT. THE PLT THEN REPORTED THAT HE WAS 'UNABLE TO GET DOWN' & REQUESTED VECTORS TO CORPUS CHRISTI. HE WAS AGAIN ADVISED OF IFR CONDITIONS AT CORPUS CHRISTI. WHEN ASKED IF HE COULD FLY AN IFR APCH, HE GAVE A NEGATIVE REPLY. HE ALSO REPORTED THAT HE WAS IN IFR CONDITIONS & HAD INSUFFICIENT FUEL TO FLY TO SAN ANTONIO. SUBSEQUENTLY, RADAR CONTACT WAS LOST APRX 2 MI SOUTHEAST OF THE ARPT. LATER, BOTH OCCUPANTS & ACFT DEBRIS WERE FOUND WHERE THE HAD WASHED ON OR NEAR THE SHORE FORM THE GULF OF MEXICO.