For seven nights, should we split between Perth and Fremantle or use one base?

Check luggage storage on the transfer day and airport travel from the final base. Seven nights give room for a split, but it should improve the trip rather than just follow an arbitrary ratio.

If moving hotels feels burdensome, choose a base near a reliable rail connection and visit the other area by day. Compare the complete door-to-door journey from each candidate hotel.

List what you will do in each area and where you want to eat in the evening. A split stay can be worthwhile if both places have several planned days.