Here is the kit I used. I had to cut a few long edges to angle (about 15 degrees or so) but other than that it fits together pretty good. The t-slots are already there so it was worth the extra $20 versus getting my own MDF and trying to cut it myself.

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https://www.amazon.com/dp/B01LX3ICXP?m=A28WGZVSH1VJP&ref_=v_sp_widget_detail_page