It's not about loading sheet goods. It's the coolers, bins, boxes, etc. that are
hard to place because *they* don't sit flat. Everything rocks or sits at an angle
making it hard to stack items.
The reason I have owned minivans (specifically Odyssey's) even long after
the kids moved out is for their cargo space. My 04 was almost perfectly flat
from the tailgate to the back of the front seats. The 06 was not as flat, but
had dips, not humps. Dips aren't that much of a problem.
My 17 has humps and dips and nothing fits easily. I can carry 10' boards but
the big hump doesn't allow them to lie flat. Same for sheet goods. They sit on
the floor at the front of the van, but point towards the sky at the rear. It makes
it difficult to load stuff on top. I made this platform to level the long boards out.
It sits between the front seats, over the base of the center console. It compensates
for the hump near the rear, but it doesn't help with sheet goods.
https://i.imgur.com/gRCgJaG.jpg
The 18's and beyond are even worse because the sliding bases of the center
row seats stay in the vehicle. Those bases (humps) are at least 3" high.
https://blogmedia.dealerfire.com/wp-content/uploads/sites/818/2019/09/MERH-mid2-0917_o.jpg
I like the way the Odyssey's drive, last, tow, etc. It's the floor of the 17 that bothers
me and now that summer is here - and my shoulder is healing up - it's time to flatten
it out. I'm considering making 3 platforms. If I split the rear one from front to back
it'll be easier for me to put in and out by myself, although it's so rare that I need the
rear bench seat. I need to think about that. I like the seamless look of the single large
platform. We'll see.