RVK fans are superb, and seem to last forever.
As above, fit it in the loft space. Ideally hang the fan, failing that bolt it to a large wooden board and place on the loft insulation (to offer some mechanical isolation, so fan vibration doesnt carry into the house).
Replace the ceiling extractor fan with a grill, run a rigid hose for as far as you can, but the connection into and out of the fan must be flexi (again, isolates vibration). Extract to the same place as currently.
Use rigid for as much length as you can reduces air noise, and keeps air speed up.. The flexi hose is great when you need it but REALLY slows the air down, traps dust and grime and makes a lot of air movement noise.
Ideally you want it to be controlled by a humidistat, this turns it on when humidity is high (ie when its needed).
This will shock you with how much air it can move!
If not sure about wiring get a sparky in to do it, ANY wiring in bathroom MUST be done by a spark. (loft doesnt...)