Spare wheel

You 'can' use a bottle jack on a caravan chassis. You just need a suitable block of wood to spread the load. Wouldn't take a lot of effort to make a custom one with a couple of battens to slot over the chassis member. Less effort than a scissor jack.

I used out wind down for the 1st time last spring in order to remove the spare for a new tyre. Getting the wheel off was a little awkward but Ok. The winder failed completely trying to wind it back up. Now we just keep the spare under the bed (same place on the floor plan it was in before, just above the floor instead of below) when stored. It rides in the car when touring to increase the caravan payload for bulky stuff. 

Sorry to reopen this discussion but filling in time have just come across it.  Many years ago in my previous caravan had a tyre disintegrate in France on day 1 of a 4 week holiday - we were living in France at the time.  Two points from my experience.  First; I have a Bottle Jack and with the wheel on its rim I could not get the jack under the caravan.  Solved this by using one of my ramps which raised the wheel just enough to get allow me to use my jack (note, for security keep the caravan hitched to the car!).  Secondly, sourcing a spare.  As has been said earlier, sourcing a new tyre can be a problem.  We had to wait 4 days for the local tyre depot, near Lourdes, to get one!  We were not prepared to drive through Spain without a spare.  So an unplanned stop in the area!  I have an Alko Under Van Wheel Carrier and yes they are a pain BUT the spare is out of the way with the weight near the wheels;  and so long as you keep it the carrier greased it is not too difficult to use and how often do you need to access it - it is greased on service and the tyre condition checked.  

I have always carried a spare wheel having seen a number of caravans on the side of the road with one wheel off and seemingly no spare.  I started with the underslung Alko carrier but gave that up because it reduced my ground clearance and was very difficult to use.  I now carry the spare wheel in the gas locker wrapped in a sheet and secured with a strap.  I have had a 2-ton trolley jack for many years and it travels in the boot of the car.

Is it necessary?  All I can say is that I have had 2 blowouts in the past nearly 40 years and both were caused by sharp pavement corners.  The first many years ago was entirely my fault but the second was in the small village of Natters in Austria and I was avoiding a car coming round a corner in the middle of the road at speed - I clipped the curb.  Both times I was glad that I had a spare.

I look on it as an insurance policy - if you have it, you won't need it.  If you have the room and weight capacity, I would recommend carrying one depending, of course, where you go.  We tend (or tended to before Covid and a new knee) to go slightly off-piste to place abroad where help is not always readily available.