I put a Leslie RS3K on one of my past trucks with a in cab under steering wheel metered train horn valve.
Put them between fuel fill and rear tire well CCLB - so room, fabricated brackets to make them fit and bolted to frame
Passenger side between cab and rear wheel well I mounted a 9 gallon air tank.
Twin viar compressors were mounted under cover in the truck bed
Airlines down the frame and up the passenger pillar, under dash to the valve, back down driver side pillar (drilled holes and used bulk head air line fittings....then back to the horns ....put a valved accessory airline quick connect under the bumper by the hitch receiver.
Was a sick set up.
Some looking around underneath and you can find room to make things work for a slick set up .... But does take some work to do a metered valve set up. But it is rewarding.