Also, having some fun finding an appropriate waste board. Being that its out in the unheated and uninsulated detached garage, I need something thats going to be stable.

I've been canvassing local shop fitters / plastics suppliers / kitchen fitters for some Tufnol 1P/13, Phenolic Sheet, or Trespa Athlon. Looking for approximately 20x800x1000mm - any quotes I get back are in the £300ish range which feels quite dear, is that expensive or about right? Does anyone have any recommended suppliers or alternative materials to look at?