Drilling a hole through the floor.

[Routemaster]

Are there two layers of wood with air space between them throughout the coach? I drilled a small hole down at the outside of the "I" beam at the outriggers. I felt space after drilling through the main floor and then through some wood where the waterproof is stuck on underneath. Is this common?
Den.

 

[Routemaster]

I sussed it out. There is the 1/2" floorboard then a large amount of polystyrene then a 1/4" board total amount of 3 1/2".

 

[travelin2]

I sussed it out. There is the 1/2" floorboard then a large amount of polystyrene then a 1/4" board total amount of 3 1/2".

If you have a bighorn that sounds about right. When I had our grey #2 out for repair, the cut out in the floor for the kitchen sink drain was as you describe