The answer is complex and insurance laws vary from state to state.. In some cases a police covering a pick up truck might not be valid once the camper is slid in (I won't go into why cause I'm not a lawyer).
Also assuming (And I stress that word Assuming) the camper is covered at all it would be covered same as the truck,, Damage and liability.. You would not have coverage for ":Household goods" inside the thing.
So you may well need a rider.... Or not... Depending on where you live.
Home is where I park it!