I think the Lexan inserts Skito offers are just disks that sit under the riders seatbones. Someone more intimate with Skito can certainly correct me if I’m wrong.
I made my own pads to go under my two treeless saddles. I purchased the Lexan sheets (I only saw one thickness, but don’t remember what that was…) at Home Depot and cut them myself (with a Dremel tool) to a pattern I had drawn that extends the full length of the pad. The Lexan was cut to the contour of the pad and a little narrower than the top layer of laminated memory foam. The edges were rounded. (also with the Dremel)
I then used my willing horse as a model, heated the Lexan with a heat gun, and moulded each piece to the shape of her back. (using a saddle pad as an interface, of course! The Lexan was hot)
These Lexan panels that have been cut and moulded to my horse’s back slide into pockets on the inside of the pad cover. This keeps them in place and helps distribute the riders weight over the full length of the pad.
I have a blog post about how I made the pad for my Sensation. I can’t share the link directly from work as I can’t access my blog from here, but if you click on the link below and search around, you should find it.