Circuit breaker fuse panel coach

If the converter is original equipment still, it probably hums more or less when it's plugged in. Maybe you can listen carefully for a 60Hz hum and see where it's coming from. Quite often (but certainly not always) the fuse panel and AC circuit breakers are at the same place, or very close by.

have to start looking in all the cupboards , normally with the 110v fuses, and the converter, sometimes under the rear bed.

They should be somewhere inside. Have you looked in every space high or low or in the back of a drawer or bottom cupboard? Good luck