Solar and battery capacity required for cabins and RVs is usually limited. As with homes and properties always have maximum solar capacity. Consider using LiFePO4 batteries as 80% of their nominal capacity is available. LiFePO4 batteries are also light and compact. Lead acid and AGMs, however, are fine for converted coaches. For those, size and weight are less critical.
For RVs in particular, space for solar modules is usually at a premium. It is thus best to use solar for lighting, water pumping, TV, laptop computer. If using solar keep compressor fridge below about 220 litres. Use LP gas (or diesel) for heating and cooking.
Buy the most efficient solar modules on the market. They are likely to be monocrystalline but the very best polycrystalline solar modules are equally efficient. Flexible solar modules are convenient – but typically produce only two/thirds of the output of the better rigid modules.