You dont want to use MDF in most outdoor atmospeheres. It does NOT like alot of moisture. Even with a “proper” primer/sealant, the fiberboard will still bloat ridiculously badly… within a matter of days.
Direct soaking? Large structural loss in a matter of a couple of hours.
MDF is ideal for indoor use, away from constant moisture. By moisture I mean excessive dampness (near a pool, floor decking in a bathroom, doghouse).
It’s plenty good for kitchen cabinetry or anything drier.
I have plenty of scrap You can play with, but nothing bigger then 10"x10"x.75