One thing you could do is build a custom embedded PC system that is essentially a laptop. You can buy embedded PC systems for lots of sources, and you can get the components pretty easily as well. But you'll have to figure out an enclosure for it all, which is the tough part. There are companies that sell bare-bones OEMable laptops, but you'll probably be better off buying one since there is a lot more effort put into making those systems as durable as possible.