So far as I understand it (and I'm always open to correction on matters electrical), the BIP unit incorporates a transformer to convert 220/240V AC to 12V DC so if you remove the transformer you will lose both your 12V supply to lights, fridge when towing, heater fan (if fitted) and taps as well as having no means of recharging your leisure battery.
What you need then is an alternative unit that will act as a charger and also provide a 12V supply. A battery charger will do only the former.
If you haven't already seen it, THIS link should be of interest.
If all you want to do is replace the transformer, I have one that you can have for the price of postage.
If in doubt, ask JohnE who understands these matters.