I replaced my cushions almost immediately after I bought my camper new with denser foam. I had them cut to the same size as stock. Made a big difference however I have one cushion's cover seam starting to split. The denser cushion will put more force on the seams since it will not collapse like the stock cushion. You need to wrap the cushion with plenty of Saran Wrap before putting on the cover so things slide around a bit. If I do it again, and probably will on a new purchase, I would take a 1/4" off the length and width to allow more forgiveness. May be it was just bad stitching on my cover, don't know but something to think about.
2016 Ford F-150 4x4 Supercab XLT EcoBoost
2012 Salem Cruise Lite 221RBXL, Andersen No Sway WDH, (2) Honda EU2000i's