Yes, spills while filling/emptying will be the biggest issue. I just don't want my gear smelling like a log truck from the fumes for the next 6 months. I'm still pondering a transfer tank in an open bed, but there are major issues off road there as well, not to mention storing gear. It sounds like, from these responses, that vapors in the canopy wouldn't be an issue assuming good cans and tie-downs. Good. Thanks!