Further Progress has been painfully slow..Short of rectifying low tyre pressures!
However, Mr Arragonis has shamed me into looking for Coroplast for making a grill block..
5 SHEETS BLACK A3 CORREX FLUTED PLASTIC 4MM/700 GSM | eBay Should apparently work (according to Mr A)
Hopefully that is enough for an upper and lower block, given that it's 3 A3 sized sheets..
Additionally, If possible, I'm going to try and offer up the e46 undertray I have at the unit- see if there's any real work needed to make it fit.