Unimog Club UK

Make two L shaped brackets one slightly longer than the other then make a rocking beam that sits under the tank and on top of the L braket to allow for flex clearance to pivot point must be a minimum of 20mm always remember to not drill or weld the chassis.
Moose

Sorry rob
The two l shaped brakets come of the chassis and the horizontals sit under the tank one of these must have the beam to privet.
If you need a drawing let me know brian may be able to find something on EPC
Moose

Hmm, we are wondering now whether it might be a better fix to remove the current diesel tank from its perch under the passenger door, and replace it with the big tank. The current tank is two feet long, 15" high and probably 18" deep. It sits inset into the checker plate side step like so:



The brackets that hold the tank fore and aft are welded to the support brackets for the side step like so:



Fastening the big tank on top of the side step brackets would work just fine as far as we can see. The dimensions are: 4 foot long, 26" deep, 15" high. The only problem is that the big tank is 26" deep front to back, so unless we can snug it right back against the chassis rail, we can kiss the step to get into the passenger front door goodbye! Alas, there are some great big triangular bracing bits that will effectively push the tank out about 4-6" from the rail Here are the big triangles:



And an overview of where they are:



Actually the two step brackets that sit behind the current tank have smaller triangles! Here they are:



And only one of the really big triangle brackets is getting in the way of the big tank, so perhaps we could remove the existing giant triangle, and get a slightly slimmer one welded in its place? Then if we lift the tank slightly off the step, that will mean it sits back further towards the chassis rail too...

What do you think guys? Does this sound do-able?
Just modifying this for a quick update.

Cheers for all the input!

Rob & Sue
 

I have one inspiration which springs to mind.... sell it!

keep the standard unimog one, and spend your time doing something else.  Aluminium and steel put together isn't a good mix without isolating it from each other to stop corrosion. 

280 lts is around 250kgs as well, so it's going to take more fuel carting it around.

Are you going to do long journeys in one day with veg oil ? As you say a lot of weight to carry as a rule Mercedes sized the tanks for one days average use surprisingly small tank if that's the case, One of the reasons the 404 has two small tanks is the flex in the chassis.
It is possible but will require some engineering and consume space.
Moose

We think that, as with seemingly everything for these fire truck 'Mogs, the fuel tank is a custom size - we were surprised by its size as we were expecting the average size Mog tank, but it's a 90 litre tank and unfortunately the way the filler spout is attached means that it's virtually impossible to actually get 90 litres in it. Barring its temporary use as an aid to our house move, we shouldn't be making enormously long journeys in it - maybe into NL or Germany for various dog events, and dotting hither and thither on rallies etc. So perhaps this is a project for another time...

Cheers for the advice guys!

Rob & Sue

Your tank looks like a 406 fuel tank If it's in good condition i'd recomend removing the drain plug from the bottom and allowing to drain for a few seconds, then put the plug back in. the reason these tanks have the little "bowl" in the bottom of them is to allow water to sink to the bottom of them, the water can then be drained as I just described. Otherwise they eventually rot out!