Hi Paul
You might want to consider the Italeri kit IT0419 Field Tool Shop as a source of additional items to add to the cargo area. Not expensive.
Shown here Alternatives are items from Plus Model. It's probably best to go through their web site to see anything that takes your fancy.
http://www.plusmodel.cz/news_en.php Another possibility is items from SB Scotia
See Steve at SB Models site for items available
http://www.sbmodels.net/ As for Tarps, various methods exist from rolled thin Milliput and other Epoxy Putty types, to tissue papers soaked in a water and white glue mix.
Alan