Exactly. Its pretty simple.
Just use some filler (for walls for example, should be available in almost every household store) and mix it with water until its consistence is pretty thick. Like pudding so to say. Bring it on the base, and smoothen it with the help of a piece of wood or use cardboard instead. First layer should be as smooth as you can get it. If you have some uneven spots.
Two possibilities: if you like it like that, just let it dry. If you want the result even smoother, let it dry and repeat it by filling the uneven spots.
Drying process can take a while, in this case 1 day (depending on the thickness of course).
When its almost dry you can add panel lines with a cutter. Pictures of original places help here, sometimes the plates arent too straight for example.
Basic rule for 1/48 scale here...
not more than 1mm.
When its all dry, add very thin washings (really... VERY thin!) with earthy tones, in my case some khaki drab. The surface will dry very fast. 2nd layer in my case was with NATO black, for the very dirty spots. If you like, you can add some clear color for wet spots like puddles etc. More contrast is achieved by additional sanding.
Panel lines itself: white glue and lack (better: dark grey) color. The lines are filled with a syringe with a small cannula.
Some small grass pieces here and there were added too (all a matter of taste, of course).
Cheap... and simple.
