If you have to use polyester resins, the usual ones that get hot, do it in layers, making sure you add the next layer as the previous one JUST starts to gel. This way the heat build-up is reduced, it is unlikely to crack, and provided the layers bond together, you won't see the joins; there won't be any. Also, you can get some depth under your model, place it on the gelling layer and add the final couple of layers to locate the model. Also again, you can tint the layers, starting dark and lightening the tint until the last layer is clear. This will give a really enhanced sense of depth. Also yet again, if the first layer is 'sea bottom'colour or 'river bed' colour, it will look even better.
Test the resin on a hidden part of your model, or some scrap material, to check the liquid resin won't attack the ink or paint, if it does yuo will have to seal the model with a polyurethane varnise.
Acrylic resins and gels are much more freindly to use, they don't get hot, they don't usually disolve the model, and they don't stink! You can sculpt very effective waves with the stuff too.
Tim P