Any updates or photos on how this came out? I need to maximize the inside space and I think you have the right idea.My dealer is installing the Front Runner Flat Tank (FRFT) to my ACCC on a 2013 Tacoma Access Cab Long box tomorrow. If possible do the FRFT mounting before the ACCC goes on the truck. Yes, it does fill that space pretty damn good. For my application, the frft outlet on the bottom will come out the passenger's side of the accc through a spigot for gravity flow. I will use the frft for outside duties and extra water capacity (maybe even shower use) Also, I will be able to easily fill the Septor 20L water can in place, the Septor will serve my inside accc water needs (morning coffee-
The fill cap area has "just" enough room to get my hand in there to unscrew it and about 1/2" clearance above the top of the fill cap after you unscrewed it. Keep in mind the panels in the fill cap area on the accc are slightly different on a 5' accc to the 6' models. (do a quick search) The YouTube guy installed his FRFT on a 5' box and commented he had to relocate his fill cap to the front flat side (check comments below his video). I will not have to relocate my fill cap location on my 6' accc FRFT install. YT guy installed his frft with the accc on the truck - so it is doable.
It looks like it may be a small effort to get a fill hose into the fill hole - but I figure in time I will find an appropriate hack for that as well. Hope this helps.
Link to the FRFT that I used-
A 40l (10.6gal) water tank that is perfect for showers, drinking, and cooking. This slim upright water tank fits inconspicuously behind the rear seat of your vehicle.www.frontrunneroutfitters.com