I have separate lines with separate fill valves. I wanted to keep the lines as short as possible and not use any fittings to minimize potential leakage. Thank you for posting that link. I watched several youtube videos on air bag installation on various cars before attempting the installation on my own.
Unlike the previous generations, current generation has the rear shocks outside of the springs. The only thing you have to remove is the hard rubber cone bumper inside the spring. This cone is bolted to the top spring mount, but can be easily unbolted by removing the nut that holds it. Getting the cone out of the springs is tricky but can be done without removing the springs. Yes, you fill up the air bags through the air valves like you fill up tires. As surgeon0 mentioned above, 25-30 psi is the pressure you want to fill up to when carrying heavy loads - this is pretty much the pressure range recommended by the manufacturer.
Without any loads and at 25-30 psi, the bags raise the rear about 1/2-1", and also make the ride bouncier in the rear. I keep the air pressure about 5-10 psi (5 psi is the mfr's minimum recommended pressure) when car is not loaded and reduces the bounciness significantly.
We have a 2500 lbs (dry) travel trailer that we tow 5-6 times a year with the HL. With the trailer hitched and trunk loaded with stuff for camping, the rear factory suspension sags badly, which led me to extensive research on means to improve the rear suspension. Air Lift offers non-car model specific kits that can be ordered based on inside dimensions of the springs. My research showed that the air bag size used in the Air Lift Sienna kit matches the air bag size recommended for the inner dimensions of the HL springs. The Sienna specific kit is also cheaper. Ride-rite by Firestone is another manufacturer that has good reviews.
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