I bought the watercolour palette for my Scout box after having the oil painting version for a while. I love the option to buy spare parts. I find that this wc palette is a little looser in the slot than the glass palette, and I may have to jam it so it doesn't rattle about when I travel, but it definitely fits, and the dimensions might even be necessary since some woods shrink and expand depending on the ambient temperature.
I also found a shop on Etsy (poemsbaoutyou) that makes 'mini' bioplastic pans to fit the P&A Petra. Though I have not received the pans yet, it seems like the Petra wells are the same size as this Scout palette. I was apprehensive to fill the trays directly as I would be stuck with one palette when I might need to swap out certain colours with seasons. Or moods. Or subjects. Or.
Shipping and service were super fast! Real glad with my Scout in general and this addition just makes it all the more versatile.