Good question....I haven't seen him move them. I'll ask.
Here's the context;
Having decided a LDT simply ain't big enough and that the arguments for a MDT pretty much lead to a HDT, the question becomes what of the deck? I don't want a smart car and I want a jeep to be readily available for scouting; ie, towed; not some sort of angled config on the truck (as they are too long to go sideways as per the smart cars).
Next, an HDT is big enough to make it a stand alone over night RV so, it would be great to take bikes along which leads to your buddies trays which leads to the choices; that or some sort of on deck deal, like they are mounting smart cars. Obviously, that would seem to be much more involved, off and on, than your buddies side car deal.
So, fleshing this out as I type, his trays seem great with only windshield height to worry about and the 'big' bikes could be in the 5th wheel garage with dirt or dual purpose in the side saddles for easy access.
AND THEN, some sort of deck above them for storage or even another bike or two; just not a readily accessible one(s).
My last hang up (for now) is that it would be great to also have stake sides for the HDT that are stored during towing and can be added on to make a quasi pick up truck for whatever when the trailer is set up.