We used the minivan as a camper van quite a few times in the summer and fall last year. In the early winter I had to replace the tires. I had run flats which had already been replaced by the previous owner of the Sienna. The van had less than 75000km on it, and it was going to be on its third set of tires! I decided to buy regular tires – not run flats. However, this necessitated buying a spare tire. The total cost was about the same as 4 run flats, but the Michelins that I bought have a 140,000km rating. Needless to say this will prove interesting to store in the van when I go camping as some valuable real estate will be taken up by the tire. Or I could take a chance and not carry it on the camping trips.
I have added some photos of the conversion on Flickr: http://www.flickr.com/photos/petergs/sets/72157633700840665/