No- I've never used the wet spray material.
There are some people that believe that its more cost effective to insulate the foundation walls and leave the underside of the floor uninsulated. Then you seal up the crawlspace vents so your crawlspace stays ground temperature- 50-55 degrees in most areas. This really cuts down on the amount of insulation you need since the footprint of your house has many more square feet than the surface area of the foundation walls. The only catch is that you must have a good vapor barrier (plastic sheet) on the ground in the crawlspace, or else moisture from the ground will rot the floor joists. Of course, in your case, maybe that would be a good thing since it will make things easier to tear down in 5 years
Are you planning to build the new house yourself?
9 years ago, I did the same sort of thing that you are doing (living in old house while building a new house on the same property). I bought a 50 year old house with some real repair issues at an auction. I initially thought I could repair it, but other people made me realize that I'd put just as much time into it as building a new house and half as much money- and yet still it would be a 50 year old house.
In 9 hard months, my dad and I built forms and poured a solid concrete foundation, framed the house (1500 square feet, cape cod style, 3 bedroom, 2 bathroom) wired it, plumbed it and did everything else except the sheetrock and insulation. It was countless hours of work, but you save sooo much money vs letting contractors do it for you. I was impressed at how reasonable and helpful the plumbing and electrical inspectors were (even though I failed the plumbing inspection the first 2 times)
I tore down the old house by hand (about 1200 square feet- single story) and was able to sell the trusses and other materials out of it for about $400.
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