Spare Tire

I am a newbie 2007 20-foot Sarari owner. Reading "The Newbies Guide to Airstreaming" I realized for the first time that the trailer came without a mounted spare tire, which is pretty incredible to me in view of the forethought that Airstream seems to apply in every other aspect of their trailers. From other threads it seems that my two choices are to buy a spare wheel and tire and throw it in the back of my tow vehicle, which I certainly can do, or do a retrofit add-on of a rack under the trailer somewhere, which I find pretty annoying after spending what even used Airstreams cost. A retrofit mount on the tongue, above the battery box and between the propane tanks box and the trailer cab seems a better solution than mounting under the trailer. Any suggestions would be welcome.