Greetings . . . My preference is heavy plastic drop cloth sold at hardware stores for painting. It's very thick and holds together well with clear packing tape. You can cut it down to whatever size you need. As Drew said - you cold spay the engine with penetrating oil to prevent rust.
I have even used the stuff to make a 'well' on my work bench so that one can soak large parts in water based degrease and/or Evapo-Rust. A few bricks and some two by fours (for support) and the drop cloth acts just like a swimming pool liner. When done one can siphon off the liquid for re-use and toss the used plastic . . .
regards,
stock49
