I have an extended cab short bed truck. There isn't much available for that configuration. IIRC I once saw a larger replacement tank that increased the capacity by something like a whole 6 gallons. Which brings up the 'bang-for-the-buck' factor. It just isn't cost effective to pay over $1000 for a tank that only gets you an extra 6 gallons.
On my previous truck I went down the extra fuel tank road. On a strictly 'bang-for-the-buck' basis, the best way of going was a 'in-bed' aux tank. I got a 100 gallon tank for IIRC around $600. I rigged up an electric fuel pump to refuel the main tank. Yes, it took up about 2' of room at the front of the truck's bed. But the truck was mostly a tow vehicle for a work trailer and never hauled much of anything in the bed.
I'm considering getting a cross-bed tank made for my current truck. I'm looking at a tank about 20" tall, around 58" in length and about 10" front to rear width. I figure it will give me about 35 to 40 gallons of extra capacity and only occupy about 10" of bed length. I think I can live with that.
FAA A&P mechanic, ex-RV dealer parts dept
Retired B-52 Gunner/Flight Examiner, B-52 Crew Chief
2016 Jayco Eagle HT 29.5 FBDS w/ 15,000 BTU AC, 50 amp service, upgraded counter top, thermal pane windows, elec. stab jacks, outside grill, backup camera and MORryde pin box.
2011 GMC 2500HD DURAMAX/ ALLISON