While a floor jack has a wider base than standard scissors jack that most vehicles with a jack have now days, any jack with a hydraulic piston can be unusable when you go to use it after many years of storage. There are at least two pistons and cylinders to the hydraulic jack section of a floor jack. The large one most people commonly think of, and the small pump one that is moved when you operate the handle. If either or both of them rust enough the jack will not be usable. I had a nice little bottle jack that I had an extra wide top welded to, and I used it for several years. Sometimes without using it for quite a while. Then one time I went to use it and it was rusted stiff and would not move.
And a scissors jack is not prone to sudden drop from seal failure like a hydraulic based jack is. That is why people use jack-stands.
The scissors jack ( though not as stable as a floor jack ) is a design that even after long storage is more reliable in regard that will more likely still operate if needed. Just inspect and lube the screw and hinges once in a while and it is good to go.
So if you do put a floor jack in a vehicle, it probably is wise to also keep a scissors jack in it as a back-up, both as a second support incase the floor jack fails while the vehicle has been lifted by the floor jack, and also as the only jack if the floor jack is not usable when needed.
