You specified a particular Suburban heater in the title - are you sure that is what you have? FEMA trailers sometimes had residential heaters rather than an RV type.
The SW10D is LP only and only uses a tiny amount of 12v. It is DSI (spark ignition) on demand, so there is no switch for lighting. It's either On (automatic) or Off, depending on 12v power to the circuit board. Normally that 12v power is switched, though, and has an adjacent red light to indicate if ignition failed (burner did not light). FEMA trailers are bare bones and typically set up in one place indefinitely, so maybe they omitted the usual remote switch? Or stuck it in some obscure place close to the heater? FEMA trailers aren't designed for daily travel, so that sort of amenity is often omitted.