If youre going for blown up there is no need to cut them in half-generaly you either find they have a big hole in them and they are burnt out or they are in lots of little bits-depends what hit them!
If youre going for the hole in the side/front/top try not to actual cut a hole with flat edges but bend the plastic in to create a hole as if the metal has been deformed by a large blast (perhaps even bend it out on the other side to show where the blast ripped through).
Maybe model a tank with its tracks thrown out in front/behind with a small blast mark on the guide wheels (mine/sticky bomb damage) and then model blown hatches etc onto it!
As for lots of little bits-plenty of plasticard cut into jagged and bent panels (painted in the correct colours then with loads of scorcting/burn marks) with plenty of recognisable vehicle bits scattered through the wreckage |