Stacking kayak on top of SUP.

Wondering what advice folks out there have regarding the safety/advisability of stacking a 17’ Titris kayak on top of a SurfTech Balboa SUP to transport. Looked for posts dealing with this specific issue, but found nothing dealing with quite the same thing. Hoping to transport one 17’ kayak on a Thule J-Hook rack, but also want to transport the SurfTech flat with the Titris kayak on top with padding between. Any thoughts?

Both on the j hook or one on j hook one on base rack?
Like this…

Or like this,…

What length bars do you have ?
With 78"bars, I can carry two sea kayaks in J cradles, (one on each side), and two SUP’s in the middle. I use wide rubber saddles on the bars under the bottom SUP and then just two pool noodles between the boards.
Each SUP has it’s own cam-lock buckle straps, and cinched down tight, there is zero movement

Racks are 55", not wide enough for both kayaks on j-bars AND SUP between. I’m thinking of putting the SUP on a base rack and stack one kayak on top of that and then have room for the other kayak on a j-hook. My concern is whether the SUP will be ok with a kayak strapped on top and/or I will be too high (the kayak being too high that is).

My opinion : I wouldn’t do it.
The tie downs from the kayak on top of the SUP will be at an angle going to the bars which if you go over a few bumps will allow them to wiggle and loosen.
They should come straight down from the kayak to the bars

If you are going to be constantly carrying these boats, why not spring for longer bars ?

Sup is likely too wide.