We have 2 Mitsubishi L200's and they have the same dimensions as the Navara.
You can fit a flat 500 litre tank with room down the sides for DI vessels and a battery box with your pump attached to that. Between the tank and loading door you will have room for two reels and two poles will fit diagonally across the top of the tank. We fit a Gardiner 44ft pole in there and a bag of extension sections if we need them too.
You can get a custom made, crash tested tank fitted if you have a cab on the back. It will hold about 620 litres. This will reduce the space you have left down to one reel if you have a battery box in that space too. Plus, your poles won't go in sideways, the tank has a couple of slots for your poles to slide into and because they go in horizontally, you can't fit as long a pole in.
We weighed it all up when we bought the first L200 and went for the first option. It works brilliantly and we have last week bought another and had our second one fitted out the same way.