Assuming you're talking about the under-the floor fuel cells:
You can run one in a daily driver, and route the filler neck into the sock location, however, you'll still have a penetration through your floor, and the fill tube running through the passenger compartment.(not a great idea)
No direct knowledge, but I have heard that some states outlawed fuel cells for no-road vehicles. Check your local regs.
You won't pass emissions. If you have the required check where you live, they'll fail you when they look at the gas cap on the OBD-II systems.(even if you figure out the check engine light)