Polly I have just been speaking with Mick about this topic and he has suggested that instead of having a complete new radio fitted, you could just have a pair of speakers installed in your lounge area and use your current cab radio/cd player, that would save space. As for using up your battery life, he says you will need to find out how much power it uses (via instruction manual?) and then make the calculation.
We had a car radio/cd installed in our caravan with the speakers coming out underneath and by the time we had a couple of CDs in there the cupboard was full. Do you have an empty cupboard spare? If you have, when you get your solar panel fitted, I am sure your leisure battery(s) would cope.