Solar panels are most efficient when pointed directly at the sun and it drops off fast as the sun crosses the sky before or after peak sun. Those panels might be maybe 10% efficient mounted like that. In other words if they were rated 250 watts, they are only getting 25 watts output mounted in that position.
True about positioning and inefficiency of poor positioning, to place them in the angle of 30 degrees have been reported by engineers far more knowledgeable than I would ever be seems to be optimum angle placement.
On houses the solar panels will vary depending on geographical position of the location the panels are placed where on mobile vehicles you need to get a general mounting that will work anywhere.
That is the main reason I mounted my regular solar panels to see if that would last with all the conditions we encounter with a truck. So far so good over 3 years later. FYI. The only problem I have had is shorting because of wiring installation that is pruely my fault for not allowing for wires rubbing against something, but the charge controller usually faults out when that happens till it is corrected.