The advantages are density of power.. Hydrogen compared to AA batteries is rather dense. The disadvantages are cost and containment (As noted by a prior poster) and where does the H2 come from?
THey split water to get it,, Ok, how do you do that? Why you take standard house power, rectify it, and feed it to a container of water via a couple of electrodes, You collect the gas that boils off ONE of them (The other one is oxygen) and you then compress it.. All this takes electricity, A LOT OF IT, relative to what you will recover.
Thus not practical for RV use.