I kind of wonder that too. I've seen a couple, but no idea who built them (maybe owner-bult). I've had half a thought to try building one myself; mine's pretty heavy (steel), half the time it's just my sled, and loading/unloading would be much easier at 3" off the ground than 5." Hopefully there are some good options out there.
https://www.kimbuiltmfg.com/kimbuilt-decks Talk to Cole @ 208-630-3720 This is what you want! I know some dealers stock them. They are built in McCall, ID. Well thought out and built product if you're looking for the single deck!
I curious as to why you would bother building something to sit in the bed? Why not just use a ramp and load the sled into the bed of the truck? I get it if you have a silly little truck but the answer to that is to own a full sized truck... I have been hauling my sled in the bed for years and never felt the need to build a bunch of junk because I couldn't figure out how to just use a ramp. Even when I had the Raptor with the 5.5 ft bed I still didn't have any problem loading and hauling my sled without the need for an in bed sled deck. Just seems redundant.
If I had enough money to waste on a Raptor, I would surely not buy one. I have 2?other of those oh so handy ramps you speak if, but with my puzzy truck, I made a hitch based bed extender and wanted to try something to eliminate carrying around ramp. Usually 2 of us meet up and use one of those things called a trailer. This was a project to make and test out. Thanks for your condescending post. Makes us all want to share ideas.