DRG ARR, THE FLT WAS VECTORED FOR AN ILS RWY 3R APCH. AT THAT TIME, ATIS INFO INDCD MOD MIXED ICING IN CLDS. THE CAPT RPRTD THE ACFT ENTERED THE CLOUD TOPS AT 5500', WAS IN THE CLDS APRX 5 MIN & ACCUMULATED ABT 1.5' OF RIME ICE. HE STATEDICE ACCUMULATION WAS RAPID, SO THEY DECIDED TO WAIT UNTIL THEY WERE IN THE CLR TO CYCLE THE BOOTS TO PREVENT BRIDGING. AFTER INTERCEPTING THE ILS GLIDE SLOPE ON A COUPLED APCH, THE ACFT WAS SLOWED TO EXTD THE GEAR & FLAPS. A CALL FOR 'FLAPS 15' WAS MADE & APRX 3 SEC LATER, THE AUTOPLT DISCONNECTED AS THE ACFT WAS DSCNDG THRU ABT 1900' AGL AT APRX 146 KTS. AT APRX THE SAME TIME FRAME, THE DE-ICE BOOTS WERE CYCLED AS THE ACFT BROKE OUT OF WX & THE ACFT WENT OUT OF CTL. IT ENTERED BANK OSCILLATIONS (UP TO 44 DEG) & ABRUPTLY LOST ABT 500' BEFORE THE CREW RCVRD, BUT THEY LNDD SUCCESSFULLY. INV REVEALED THE RECENTLY TRAINED CREW DIDN'T GET SUFFICIENT TRAINING IN USE OF DE-ICE EQUIP FM COMPANY INSTRUCTORS, WHOWERE TRAINED AT THE FACTORY. AFTER THIS INCIDENT, THE MANUFACTURER REVISED THE FLT MANUAL TO PROVIDE MORE SPECIFIC INFO.