Mercedes radio

My Malvern has a decent sound system. Great while driving, not so when on site as it shuts down after a short while. I understand why it does this but frustrating not to be a able to use the system while camping.
Is there a simple solution?

I've fitted a regular car radio in the hab area like this, next to the wardrobe window.[You must be registered and logged in to see this link.]


The aerial is fitted on to a bit of aluminium bracket I made up inside the cable riser at the back of the wardrobe. As radio signals pass through the outside wall they will be picked up by an aerial sited inside the cable duct. This antenna is a powered one so +12v and 0v need to feed it, and two of the many hundreds of wires inside there will provide that. I have sited the antenna as far away as possible from the wiring loom so the wires don't absorb all the radio signal. Also of course I have bunched the wiring loom in as tight a bundle as I can and secured it as far from the antenna as posible, while all the time keeping the whole kit and kaboodle inside the vertical ducting. 
What I haven't done yet is to connect a DAB antenna. I think that needs a ground plane, because usually you would fit iit on the windscreen with a sticky bit of aluminium foil stuck to the metal windscreen pillar behind the plastic trim. As there isn't any metallic surface to stick it to in the wardrobe wall I will just have to stick it somewhere, maybe I'll stick a large-ish bit of aluminium foil inside the duct and see if it works. If it does I might do an article for MMM. The loudspeaker wires feed from the radio back into the wardrobe duct, up inside there to the ceiling, across a short distance to the nearby loudspeaker, and the other one across the ceiling through the air conditioning unit to the other loudspeaker. Thus wired, the front speakers get the radio signal as well as the habitation speakers.

Inside the wardrobe, panels are restored so nothing shows:
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The slot at the top of the trunking is where some useless bit of kit was removed and sold. I think it was the satellite dish stuff, for which I have no use. I ripped it out and sold it, and fitted an additional solar panel where the satellite dish was on the roof.