Well, the model number was no help, but I went underneath the trailer and found the manufacturer and model # of the tanks. The manufacturer is Inca Plastic Molding Co in Ontario, CA (about 40 miles from here!!) I called them and they gave me the details: Black tank is 40 gal, grey bathroom tank is 45 gal, and kitchen grey is 32 gal. Eureka!
Now I have to do some research on the model number.