You could use something like one of these

Metal Stone Skirting for Mobile Homes
Mobile Home Advantage

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http://s248.photobucket.com/albums/gg177/scareisburg/

How about this, go to home depot or what ever and buy some sheets of foam. the kind that they use on the outside of a buliding. You can cut, carve, sand(60 grit) what ever you want into it. After that coat it with a roof coating (cool seal) that will kind of incase it it rubber. Than paint it.

What you will end up with is this, a removable wall cover that you can stick (velcro) to the out side of the building that you can take down and store inside after halloween.

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I was going to suggest trying out Rhinoliner if you're worried about durability and weatherproofing... Rhinoliner is the stuff used for truck bed liners... it is a rubberized textured coating and I suspect you could paint it as well... it would give you a stucco look..

My crypt is made of pieces of wood as a frame and then foam on the outside. The walls can be torn apart for storage. And it takes the weather just great.

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http://www.hauntseeker.com
http://www.planetgravemarker.com
Main site http://www.deathtouch.hauntseeker.com/

Thanks guys!
I swung by RONA the other day and found a stone type of 'paint' that I think might work. Apparently it can be used on cement, wood, as well as a bunch of other surfaces and has a sealing property. I saw it on a bench and it looked really nice and very durable. If you use it on outdoor stairs it will supposedly survive shovelling. (We'll see.) Now I just need a few days without rain or blistering heat to do it. It's like some kind of curse; it's either been +30C or raining sideways since I bought it!

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Something wicked this way comes...

Wicked is that the Rustoleum Stone Effects Rollon that they are selling for like 45.00?

I know i used similar stuff 2 years ago from Home hardware ( the 3 step stuff ) on my front steps and it looks great.. Survived shovelling for the most part.. it has a couple nicks and scrapes but for the most part its surivived.