Water pump replacement in AS Symbol

Replacement water pump options?
Does anyone have experience of changing the submersible in tank pump to an external diaphragm pump?
Our AS symbol 2019/20 model van is fitted with a 12v submersible fresh water pump and located in the rather inaccessible underslung tank. It’s not clear which model the existing pump is and Marquis can only tell me it’s one of the 12v submersible Whale pumps and there are at least two versions. It is all working at the moment but has got both noisier and less powerful as I’ve had to lower the pressure switch setting over the last season or so. Therefore, I’m considering of replacing it with either a Shurflo Trail king 7 l/min 20psi pump (as suggested by Marquis) or a Whale Universal 8 l/min 30psi diaphragm pump. This would be above the tank and inside the van under the seat/bed area so easier to maintain. I know it’s not particularly easy as the tank needs to be lowered for access to remove the submersible pump and the wiring will need to be modified as the existing whale pressure switch would become redundant. I can do all that but does anyone have experience of this? How noisy is the diaphragm pump and is the system better at 20psi or 30psi (30 seems a bit unnecessarily high to me)?

You don't need to remove the submersible pump, so no need to drop the tank. Use search facility for loads of info. Also look at Factsheets (half way down home page) , you'll find a factsheet on the fitting of a shurflo to a Nuevo, obviously different van but principle is the same.

Thanks guys - looks like the consensus is a Shurflo 7 l/min 20psi pump is a sensible option. If I can draw water through the existing submersible pump as has been a suggested makes the job a lot easier. I've had a conversation with both Marquis and AS and both offer this as an option. Although interestingly niether can tell me exactly what the specification of the pump I have. Ive ordered a pump so will play with the plumbing options and report back with a photo if I find a neat way to fit it all in the Symbol. 
As pointed out above the factsheet section is excellent - I spent some time getting sidetracked and picking up all sorts of snipits of info.