I looked at my copy of the 2000 brochure, and I think your furnace is under the refer, if so there should be a panel which can be removed and cleaning could then take place. If you are not certified in furnace repair, don't take it apart, just try to blow it out using no more than 40-45 psi of air. A can of PC air works too, however, make sure the unit is off, some PC air has different properties, so an air compressor which is dialed down to 40 PSI or so would be best.
Monty & Janet - 2007 Alpine APEX 40 MDTS
S/N - 75715 - Retired - Master Certified RV Tech