Evening folks,
In answer to the questions above:
Personally I much prefer the Celluclay
Light and easy to work - I pushed some of it around with a stiff paintbrush on this base when making the holes.
Can shrink considerably if mixed too wet and does crack slightly when drying out on thick areas - not too much of a problem though if applying a top layer of sand, soil etc.
Can be a bit messy when mixing as it is powder - I ended up grey when my Gorilla glue got an airlock and suddenly shot a burst of air into the mixing pot and showered me with the contents!
I have tried Das Pronto (grey) once - it went in the bin
Plaster can be ok but heavy, chips easily and sets rapidly
For small areas I like Wilko brown wood filler - premixed stuff in a tub. Works better than ready mixed stone type fillers
Barbed wire - I made it from aluminium diamond mesh sheet like you buy to fix holes in car bodywork
It is a little large for 1/72 really (should be really tiny) but it should still look the part once painted. Probably better suited to 35th but the sheets tend to be about 250-300mm so the continuous length that you can make is limited
Basically you slice down each side of one of the 'bars' of the mesh leaving little pointy stumps - easy as that
Make sure you cut the right way though or you end up with a collection of aluminium X's - guess how I found that out
A bit of trial and lots of error