Fuel milage

I've no idea why 5w30 stops there, it could be a drawing style, maybe more research is needed.
ETA:
http://oil4motor.com/en/cars-oil/TOYOTA/Hi-Ace-Regius-(1KZ-TE)-(D---Diesel)-(1995-)/14251

You could start with 0w40 as that should be safe under all conditions. I've used that in a lot of engines.

I didn't spot the roofrack and spots. They are great at soaking up a lot of fuel.
https://travel.stackexchange.com/questions/26048/how-much-do-roof-racks-hurt-gas-mileage#26049

Awning shouldn't make much difference as it goes lengthways.

Super-diesel is good stuff but expensive, try a tank and see if you get more miles / £ from that, I have heard some supermarket stuff hasn't got as much energy in it.

@Andonic
On the 5W-30 thing. Oils have changed a lot in the 20 years since the spec was written.

If you look at just the 'hot' grade the chart notes that 30 is correct right up through the temp scale. The hot rating is the grade that applies at engine operating temperature and if your cooling system is working correctly the ambient climate temperature won't change that operating temperature. So given the 30 is correct then the cold rating is the critical one for your climate to ensure oil flow at start and warm up.

So any xW-30 is suitable so long as it's diesel rated CF, CF-4 or better. (CJ-4, CI-4, CH-4 are all current ones I think)

It just so happens these days high quality synthetic 5-30, 0-30 and 0-40 are available for great prices and they are maintaining their properties for even longer service life.

Andonic
Just noticed from your post in the Shocks thread that you have the 1991 3L motor which I'm thinking is the "3L" 2.8Liter non turbo. If that's the case it may pay to check the spec on that motor. I know some guys even run up to a 50 grade in that engine but it could well be that 30 is fine. That chart I posted is for the 3 liter 1KZ-TE.

Andonic
Here's your 3L Service manual. Page 132 has oil spec.

http://www.4x4brasil.com.br/forum/attachments/frota-4x4-brasil/511949d1442407654-hilux-sr5-2-8d-sonho-realizado-2lt_3l_engine_repair_manual_supplement.pdf

And the relevant oil chart. Note the older API of CC, CD - highlighting the age and development of wherewe're up to with present day oils.

Interesting the range of *-30 oil.

Straight 30 is very stable: Lawnmower oil!
Maybe 5W30 used to degrade with temperature back then? They have dotted the lines but it does seem quite different from the straight 30 that basically says 'any heat'!