I agree with the other posters about weight concerns, if you are under weight capacity and still want extra fuel capacity why not look at a AERO TANKS 60 gal direct replacement fuel tank. That way you won’t have to move the camper back.
This tank is an Aluminized steel direct replacement tank for the factory plastic tank, you use the stock fill and your stock fuel gage still works and it has a drain plug.
I have had one on of each of my last 2 D/C trucks, see sig. Just remember to ask Aero Tanks for the weight of the tank and that Diesel fuel weights about 6. 3#/gal.
I think that their web site is- aerotanks.com