We just finished putting the mesh on our vents - we have a JB DRE 19'6". We did the two fridge ones the same as this video. The one at the bottom of the door - we unscrewed - it comes off in two pieces - we put the mesh in the middle. The one above the window near the bed (which says never cover as it is needed as air for the stove) - we unscrewed from the inside and put the mesh behind. We pulled the microwave out and used double sided tape and then extra tape to secure it to the vent (on the inside). We don't think they will get in the vent for the range hood. There is also a vent outside the shower, but we have no idea where this goes or what it is for, so we aren't covering it at the moment. So we have managed to do all of them without using magnetic strips and they are permanently on so we don't have to think about it (hopefully!)
So that the small ones line up, you could put the two magnetic strips together, take off the backing tape and press the screen to it, then take it off and trim
I see JB short changed you, you need to tell them to install the diverter shield on the top of the fridge on the next service. It is there to divert the hot air from the fridge out the top vent and also to prevent the top of the fridge filling up with dust. they only seem to install the diverter on every second caravan. Also it will pay to block the vent for the rear of the shower as it will fill with dust, then install an internal vent.
