Thanks for the feedback chaps.
Got hold of a 1/56 LVTP-5.
It's a 3D print; in my naivety I assummed it would have been printed on an SLA resin printer whereas this was FDM and a bit of a shocker at first glance.
Once I worked out what most of the shapes on the top were suppossed to be I chopped them off (other than the engine housing bit which wasn't there), and marinaded it in filler, then attacked it with sand paper.
Got to the stage where I realised smooth was not going to happen, so added back the grab handles with wire; covered most of the top in 'sand bags' & stowage. Then mud all over...
@ Russ; I do seem to have got a tad carried away with all this Nam stuff, but it's keeping me out of trouble... Got a few more sections of trench on the go: a corner 90 degree turn with small bunker, gate/barrier with bunker, a couple of trench end pieces and a howizer emplacement (waiting for model to arrive) and may do a landing pad, if making sand bags doesn't make me turn to drink first..