RV "Oscar" rivets, otherwise known as blind rivets, work well for light to medium weight items and are very strong. I've used them for towel bars, TP holders, coat hooks, etc. For medium - heavy items, secure to studs. A nice thing about these rivets is that they have a rounded head and shouldn't damage wiring or penetrate piping. Just drill a hole deep enough to go through the 1/8" luan plywood.
Wood screws can be used for lightweight items.
You can drill a small dia. hole like 1/16" or less and push the drill through by hand, or a piece of wire or small nail to see if it hits anything. A small dia. hole won't be very visible if you have to abandon it. If you have a fiberglass sided unit, there may only be studs/framing in the 4 corners and nothing in between. Interior studs can be found by pressing against the wall until the luan doesn't flex. Then look for the tell-tale tiny staple holes running vertically. You will also find a thin tape over the luan where adjoining sheets butt together.
In some cases, you can pull off a light switch, thermostat, receptacle, etc. to see what is inside a wall cavity. Interior partition walls are typically 1 - 2 1/2" thick. Look for plumbing vents on the roof and they will give you an idea where they will be inside an interior wall.
Or do what the factories do - use a couple of itty-bitty, teeny-weeny U-shape staples. :R I've found a lot of sharp pointed #8 x 1" screws rammed into walls and ceilings with little regard for what is behind them.