Hard drives can be operated either flat or on edge (any of the 4 edges) upside down or not.. Angles can be a problem on some drives but most drives do not mind being on edge as long as they are not in motion.
And if you are bouncing down the highway on edge may be better (or not depending on which edge) than flat epically if it did not park properly. DVR heads may never park properly since it is never truly off.
Some of the heat sinks may not work as well on edge, but ... Air circulation fixes that.. Make sure the compartment is properly ventilated (many are not) and cooled.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times