Usually the green gooey stuff will only fix a tire with a small enough hole that you could probably still air up the tire with the compressor and still get to a garage to fix it without actually needing to use the green gooey stuff. The bigger problems that seem to get mentioned are blow outs or tire disintegration and no amount of gooey stuff is going to fix that. The gooey stuff is supposed to only be a temporary fix, although I guess you might get a few more miles to the garage you want if you did use it.
As the above poster said though, if you have a tire pressure monitoring devices installed or built in the stuff will ruin them.
Most manufacturers of large RV's omit the spare tire cause they don't want an owner trying to jack up anything that huge to replace a tire, hence the popularity of roadside assistance with tire plans.