Hello Colin,
The Carver cascade 2 is no longer manufactured, so you would be hard pressed to find one that was guaranteed. There is a model called a Henry which is almost identical to the Cascade, but the majority of caravans are now fitted with the Truma boiler.
None of the models are a direct replacement for the Maxol, so some engineering will be needed to fit which ever morel you choose, but for your safety have all the work done by a competent gas fitter.