Yeah, MDF isn’t the greatest structurally. I use pocket hole screws specifically, so there is minimal splitting since they are “self tapping” to a degree. Pre-drilling would be a good option too just to prevent splitting. The MDF top is so heavy that just 4 screws in the corners hasn’t been an issue, it’s mostly to keep it from shifting/ rotating, not to “hold it down.” I’ve only screwed it in and unscrewed it a couple times, but I could always countersink a few new mounting holes if I needed to (deep enough so I wouldn’t hit them with the bit if digging into the spoilboard.)
I used glue and a million brad nails to attach my hardboard skins to the MDF. And glue and brad nails to build the MDF box as well.
Box build pics: Successful LR2 to LR3 Upgrade in Seattle! - #2 by coinbird
Up on wheels: Upgrading LR3 to LR4 in Seattle - #28 by coinbird