"it is probably heavy to get up there! How do you secure it?" On a previous DP I put it around a vent in the center of the roof. Did not fasten it down and learned that you need to put a short piece of rubber hose under it so you do not get water down the vent... it rode that way for 30K miles and saved me several times. I was able to pull a unmounted 275/22.5 up the ladder using my 30 amp extension cord as a rope.
In the picture above you can see one end of the strap that holds the tire to the ladder... the other end is under the tire although the lip at the back is probably enough to hold it in place. I do carry the jack and the tools necessary to change a inside tire if necessary. Changing a outside tire is fairly easy as you do not have to take the rim off. If in the middle of NoWhere I'll change it myself... otherwise road service. At home I use my BobCat to put it on the roof. The tire is used but it does have more tread than what the picture shows. In a couple years I'll replace it with a newer used tire.
PS: I carry four fire extinguishers... three inside and a large foam one outside.