Lol I should of seen this thread earlier I know all about rugged pcs as I was planning a build a while back that needed to be waterproofed and extreme heat. Yours sounds a little simpler so I would use a car pc case if budget is an issue:
KustomPCs.co.uk - VoomPC-2 CarPC Case
If your looking for slightly bigger there was an mcubed case think it was called a borg that has basically a huge heatsink about micro-atx sized