Finally I found a friend that could print in 3d a 28mm scale MOBAT tank for a fair price (14 euro, and no shipping cost).
Then I tried to clean most of the unpleasant printing lines with sandpaper for a smoother surface.
The wheels and interior of the tracks were still too rough, then I decided to paint them with black, hoping to hide most of the roughness.
I had not some gi joe decals, then I tried to print some copies of the original stickers and then repaint them. The final job is quite good.
I'm planning to use it in my Pulp Alley G.I. Joe leagues:
MOBAT Tank (10pt)Armor 2 Size 3 Reliability d10 Passegers 4
Vehicle (Enclosed, Md. Armor, Md. Gun, Lt. Gun)
Medium Gun (Turret, Rapid fire, Advanced, Piercing)
Light Gun (Turret, Advanced)
More (Glacis, Reinforced, Lumbering)
a picture of the unpainted tank with an unpainted modified HISS tank