I would have a very hard think about it. Think what sort of fishing you will mostly be doing. If you will be in the creeks casting lures I would keep the tinny, but if you are partial to bait, and want to do a bit of open water fishing, I would take your dad up on his offer.
I'm going to assume the move to Darwin is permanent? If so, try just taking the tinny, and if it doesn't suit your style in Darwin, then take the old man up on his offer.