Best fastener to rpod floor

I need to attach a circuit breaker and an inverter to the floor of the rpod.  It's not a very dense material so I assume some type of anchor would be best.  I did remove one of the cable clamp bolts to see what Forest River was using and I was surprised to find they use self tapping screws which would be fine in the metal frame but don't hold all that well in the relatively soft floor material.  What did you other modders use?

I bought some 3 inch 10-32 machine screws and put them all the way through with a large washer and a nut.  I used these to secure the inverter and the circuit breaker for the inverter.