Mine regularly has 2 downhill bikes and 2 hard tails, the clamps are shite, fine on round tubes or if you can position the bikes to clamp seat tubes/post but that’s to much phaff for me so I modified mine, I replaced the 3 fixed clamps with Thule style from a euro rack, the wide ones that are designed for irregular/hydroformed/oversized tubes, only problem I had was the threaded rods are not long enough to take the Thule clamps so I got a mate to machine up stainless threaded rods to suit.
Other mod was the wheel straps, got so used to using the thule ratchet type I replaced the crappy nylon straps with the thule type, so much easier with 4 bikes on.
Another tip is if you turn the bars parallel to the frame on the first 2 bikes you can still have the roof up whilst the tailgate is open, although not with double crown boxxers fox40’s etc, single crown fork is fine on my van but it’s close so check.
I learnt the hard way, didn’t have downhill bikes on but a bike with a lefty and forgot to make sure bike was on the correct way round, arrived on site opened tailgate raised roof, expensive!