2017TRD off prem 2row +cargopull; Best ideas filling deep gap for my exped/futon

Hey All,
More of a lurker than offering up as much as I should but still learning and frankly spend a ton of time on my spine issues.
To the point- it seemed to make sense to remove my back seats (2 row) as I am 5'11"+ and also my wife's gotta fit (no issue there).

I thought I'd order a nice water tank like on frontrunner I think it was and so on which I'd hope would fill that drop/gap from the flat of back to the front seats.

I am more handy with wiring and such than building up a storage area below using wood/etc. TBH.
Anyone done this and flatten it out to put between my wheel wells (I don't want to do the "coffin" stlye no height) with affordable or at least provides a needed function like the water storage and not just stuffing it with padding?

I see Goosegear does have the "stealth" cover that would probably rock but wow- $1300 basically. I am slowly doing this project and I need that $ firstly for the bedding and the electric, etc.

I just ordered a Exped megamat duo that's about 41" width (I have 2 Expeds which originally sounded good since I could jam them in- they are nice but not enough 4 my spine). I was going to add perhaps a cheap futon rollup and use those other single Expeds at the base and take it from there.
I am also getting quotes for custom foam that I can fold which would likely be my best bet for my issues- I would just return the new Exped not using it if I like the price. Problem is that they will be in pieces but not a nice vinyl seamed folding cover which I will also need for foam.

There is a big drop/gap from the flat to the back seat console minus the seats which gave me more length for my legs. I also created a big issue and heck if I want to reinstall them to be honest.

You may say WTH why r u doing this but I can't do a tent no matter the set up / cots / etc. I love and lived for the outdoors so outside of me suddenly finding a deal on a used SMALL camper/teardrop- that's where I am at. I tried to get a off road camper (I don't do campgrounds in CO, dispersed thx) but that's proved to be a nightmware and liken it to a car dealer.

Any thoughts, suggestions- I am grateful. I can get pics/dimensions but I am guessing you now what I am speaking to.

Items I will need- water storage, eventually a self rigged cabin power system I think (was gonna do a dual but...) but I do have a 1800W Ecoflow Delta and a E1pro which should get me started, some lightweight shower or fold out easier to use kitchen platform, etc.
I used to backpack, rock climb- so I am used to roughing it but my spine isn't so much (2 failed fusions). I don't give up easily though.

Again THANK YOU helping me enjoy CO again and not at campgrounds. I love my 4Runner and don't have $ for a larger vehicle nor want one.

 

Welcome from Arizona! Post some pics of your build when you can.

 

Well I've not done much yet (hurray warranty is up- odd to celebrate eh?) outside of some junk bullish bar, yakima loadwarrior, ceiling netting, pedal commander when they were <$100, led lights, a carista (how impressive), etrailer hatch tent, K&N air, and some other things that I cannot recall at 1 am with this headache.
Here are a couple old pics but also the back now that the seats r gone where I'd like to use for storage/my feet/ and figure out a useful way to fill it like a water tank or such. Just ordered the exped duo/futon/and such- Thanks