I've got long legs and stiff knees, which makes kneeling and getting up a bit difficult. Looked at some kneeler/seat things that looked rather flimsy and decided I didn't need the seat– just the kneeler. I'll use it in the outdoor garden and in the greenhouse.
So– I fossicked about in the garage and found an old cupboard door of mahogany-faced ply. From the box of leftover raft frame parts, I selected some SpeedRail joints and cut two pieces of aluminum pipe. Had a nice, thick old kneepad. So it fell together nicely.