GMC Tow Truck fuel tank?

[Andrew D the Jolly Roger]

Working on a partly scratchbuilt GMC tow truck, subject shown here.  Where would the fuel tank be exactly, and are there photos to show the arrangement that might have been used?

In the second photo, right side, you can see the fuel door is the cap just behind the driver's door handle.  Thus, I'm assuming the fuel tank would not be behind the rear suspension as usual in a pickup.

 

Apologies if this is considered common knowledge; I usually do aircraft.....thus I defer to y'all, the experts!

[Ace-Garageguy]

The cabs with the filler in that location, I believe thru '72, had the tank behind the seat...IN the cab.

The tank is installed on-edge, as below. The hole in it is for the sending unit that drives the gauge.

[Andrew D the Jolly Roger]

IN the cab???  Holy smokes....

Glad I asked; thanks so much, I appreciate it! 

[Ace-Garageguy]

15 minutes ago, Andrew D the Jolly Roger said:

IN the cab???  Holy smokes....

Yeah...could be kinda thrilling if you got punched in the side...

The next year, GM mounted the tank outboard of the frame rail behind the cab, and later still, inboard of the frame rail behind the cab.

[Andrew D the Jolly Roger]

Jeez, I'm glad I asked.....I almost messed this up badly.

Thanks again!?

[mchook]

Yup, right behind the seat & the gas cap is behind the drivers side door handle. I built this version years ago.

[espo]

While the in cab fuel tank was common at that time I think most of the rigs with specialized beds also would mount saddle tanks that held more fuel on either one side or both depending. Ya the old "Fuel tank in the cab" did more to stop smoking and prevent lug cancer than anything else. Think about it.  

[Andrew D the Jolly Roger]

I was wondering about a sort of saddle tank arrangement, yes.

mchook, I saw that, terrific work, I was glad to see I wasn't the only one who liked the GMC version.  I tracked five different tow units used in the series, and that one for some reason is my favorite. 

[Ace-Garageguy]

5 hours ago, Andrew D the Jolly Roger said:

I was wondering about a sort of saddle tank arrangement, yes.

Engineering an auxiliary tank arrangement isn't difficult, and they are common on this series of truck.

The pinched bedside on your wercker photo would tend to preclude mounting tanks outboard of the frame rails, but there's plenty of room under those trucks to mount tanks inboard of the rails, between the rail and the driveshaft.

That's where the OEM tank is in my '89 GMC.

The auxiliary filler would be in the side of the wrecker bed in that case.