We have been towing this thing all over the country for the last couple of years without a spare wheel. We have just had a bottle of goop and a 12v pump in the tool box. I have always been worried about not having a wheel and getting stuck out the back of nowhere with a shredded tyre.
I didn't want to mount a wheel on the tongue, preferring to mount it behind the axle. The ideal position I am looking at is under the floor, just behind the left wheel. (That is the curb side here in NZ). A full size spare was going to hang too low so we have been looking for a space saver. Stupid thing was that even thought no one seems to like these things the $10 - $20 ones were the wrong stud pattern and the ones with the correct pattern, people were wanting silly money for. We finally managed to acquire one for nothing. It is only about half the width of a standard wheel so will only hang about 50mm below the frame, plus 22mm for the carrier that I am making.