What's this in the floor of my van?

[Spailpin Fanach]

If found what looks like an inspection hatch in the floor of my 1989 1.6TD Westy, pics attached. It's under the rnr bed. I unscrewed the cover and found bare metal. Looked under van and just bare bare metal too. I'm thinking it might be space for diesel heater, the panel on vertical might be air input. Is there a single metal skin here or it it a double skin? I bought a 2kw Chinese heater recently and will install as soon as I have electrics sorted out. Oh yes, I'll vacuum the floor. Soon. 

[clift_d]

Assuming that this is the side nearest the sliding door, then that will probably be related to an optional heater install. The heater would typically be mounted in a protective box outside under the van, with both the air feeds and cables passing through the area under that blanking panel. The cold air feed to the heater is pulled from the van interior through the various gaps around the bench, and a low level plenum vents hot air into the van through a slot grille at the front base of the bench. The blanking panel on the side wall is probably to allow the cable run to a heater controller that is typically mounted on the side wall above the bench arm rest.

[jrt]

I have the same size hole in my floor by the sliding door. It originally had a Carver heater attached to the cupboard behind the passenger seat.
David.