Expanded or Aux fuel tank for 1st gen tundras?

Same problem we always have with 1st gen tundras: Finding someone who makes aftermarket parts to upgrade with.... this time I'm trying to find someone who makes an larger/expeditionary fuel tank to replace my factory fuel cell. I've seen some for 2nd and 3rd gen tundras (Transferflow), but yet again, nothing for 1st gen's. Any suggestions from the crowd??? I've read a lot of discussions about home-shop projects fitting cannibalized tanks that are small enough to fit under the bed where the factory spare tire would normally go and using that as an auxiliary tank, but obviously that involves creating a whole other fuel port and most of those aux tanks feed/pump directly into the main fuel cell, not directly to the engine, plus I'd rather just have one larger cell. I have an incredible amount of spare room under the bed behind the axle since my spare tire and exhaust tips are no longer located back there, so IDEALLY I would much rather just swap out my factory tank for one that expands towards the center and rear of the vehicle (I could easily fit another 50 gallons under there before I'd had to start worrying about weight/balance). If anybody has cannibalized something like this that fits under our trucks, that would be awesome to hear about...
2003 Toyota Tundra SR5, iForce V8
Dirty Deeds Industries custom exhaust terminates in front of rear right tire.

 

I've done quite a bit of searching and there's definitely nothing that is a "bolt-on".

Not sure who's going to be the first to figure it out but the best case is finding something close and modifying to work.

 

i believe the only route thats really out there would be having a custom fuel cell made.. but packaging may end up making it smaller than the OEM because of the shape of the OEM tank utilizing space pretty efficiently

 

'' most of those aux tanks feed/pump directly into the main fuel cell, not directly to the engine, plus I'd rather just have one larger cell.'' FYI...that is NOT the way Most Aux Tanks work...sounds like maybe you are thinking about Transfer Tanks , like you would mount in the bed of your truck ! If you add a 2nd tank and have it set up right....with the flip of a/one switch or toggle your new fuel pump will switch which tank it is pulling fuel out of , if your engine is equipped with a return fuel line it will which tank the gas that was pumped to the engine but not used...back into the tank it was pumped out of and it will switch which sending unit your stock gas gauge is getting it's info from so that your gas gauge that was showing empty is now hopefully showing that your aux tank is FULL. So I can not help you on what aux tank will work on your Toyota but hopefully I shed some light on how it should work when you find it/one. I will check with my old tank suppler and if they offer anything that will fit I will let you know. Good luck BLUEMIDGET