I wouldn't know old boy, is 400mm x 400mm x 12mm, MDF, for £6.50, expensive? I see that there's a 50% deposit for orders over £20, seriously doubt it'll be over that, £20 or so, is probably what it would cost to get around town here, to find and then bring home the blasted things, which in the end would be easier with a taxi...
Maybe add a few mm, as a blast pen is to be made, mounted at an angle....
Question is though, were different blast pens used at the same airfield, old empty cans (filled with sand), sandbags, limestone and corrugated sheeting....
In this case No. 185 Squadron at Hal Far (Stenborg) and No. 249 Squadron at Ta' Qali (Beurling)..
However here you are a close up shot of the Malta soil. It is brick-coloured , often almost red. So you will have to paint your sand , unless you can find a red one.