SMA PLT DSNDS BELOW 1000 FT OVER CITY ON APCH TO LNDG DUE TO WX FACTORS.

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DEPARTED VFR FROM HHR TO SHOOT SOME APCHS AT CHINO; EL MONTE. DINNER AT VNY ARPT. REQUESTED WX FOR RETURN FLT TO VNY FROM HHR FSS. HHR TWR CLOSED; LAST WX SHOWED 3000 FT SCATTERED 1 HR PRIOR. LAX WX WAS JUST BEING UPDATED BUT APPEARED TO INDICATE MARINE LAYER MOVING IN. DECIDED TO FILE TWR TO TWR IFR WITH HHR CLRNC DELIVERY. WAS TOLD THAT THE WAIT WOULD BE GREATER THAN 1/2 HR AND WAS ASKED WHETHER I WOULD GO VFR THROUGH LAX CORRIDOR. PROCEEDED VFR OVER LAX (CORRIDOR 3500 FT SBOUND). I OBSERVED MARINE LAYER HAD MOVED IN OVER HHR ARPT. LETDOWN OVER TORRANCE (REMAINED CLR OF TORRANCE AIRSPACE); NO ATIS AVAILABLE AT HHR. PROCEEDED UNDER CLOUDS ALONG I10 FREEWAY AT ABOUT 1000-1100 FT. WHILE NAVING AND REMAINING CLR OF CLOUDS DIRECTLY OVER THE FREEWAY I BELATEDLY NOTICED THAT MY ALT HAD DROPPED TO 700-900 FT PRIOR TO LNDG AT HHR. NO DANGEROUS SIT EVER EXISTED; BUT I DID NOT REMAIN 1000 FT ABOVE THE CITY AND THE CEILING AT HHR MAY NOT HAVE BEEN GREATER THAN 1000 FT AT THE TIME OF LNDG (APPROX XX30 PM). TWR WAS CLOSED AT THE TIME OF LNDG. CORRECTIVE ACTION: SHOULD HAVE JUST WAITED FOR MY IFR CLRNC TO COME THROUGH (GREATER THAN 30 MINS); AIR FILED OVER TORRANCE FOR AN INST LOC APCH OR TURNED BACK AFTER OBSERVING THE CLOUD LEVEL. APCHING 1000 FT (WAS TOO INTENT ON NAVING AND KEEPING CLR OF CLASS B AND TORRANCE CLASS D AIRSPACE.