Finally done. This is a project and modification I have been looking forward to for awhile. I've really enjoyed just about everything with my tow vehicle except for one thing - towing fuel range. Fixed that recently with the install of an auxillary gas tank.
My vehicle is a Lexus Land Cruiser 200-series, also known as a Lexus LX 570. Stock fuel tank is a 24.6 gallon. Which combined with some modifications of larger AT tires, taller profile, and towing my AS Ocean Breeze 27FB, results in a tow range of ~230 miles @ ~11mpg. While still keeping a safe margin of fuel.
Just successfully added an 12.5 gallon auxillary gas tank, for a total of 37.1 gallons onboard. What a game changer. With ~365 miles range, no long do I feel constantly tethered to the gas pump.
I realize that many models won't have such options even in the aftermarket. Fortunately in Australia, the Land Cruiser is the go to Outback overlanding and caravan towing vehicle. So they've developed solutions for various size aux tanks including a 14, 28, and 40 gallon tanks that have been recently imported to the US. Lucky me.
There are several other off-road oriented SUV and trucks that have tanks available including Jeep, Land Rover, Toyota models. Might be other companies that cater to your model so perhaps worth some exploration.
Just a couple shots of the install which was rather involved. I wanted to keep my full size spare tire mounted, which allowed me only the choice of the smaller sub-tank. It fits in the tight void within the frame, between the body and spare tire. Larger tanks would require the addition of a rear tailgate swing-out to relocate the spare tire.
Replacement dual filler neck
Aux tank gauge and transfer pump controller just peaking out behind the steering wheel.