Idler adjusters (Track Tensioners) for the Panzer4 are a very good idea and I have fitted them to all my PZ4s BUT any study of photographs of Panzer 4s in the field show that many Tanks ran with the tracks quite loose,
What has to be remembered is that in service the PZ4s max Highway speeds were approx 35/42 Kmph (20/28Mph) and far slower off road so throwing tracks was not a common occurance,
Our 1/16 Tanks throw tracks because we run them with the original Heng Long/Taigen/Torro Gearboxes which are not scale unless you really think slot car speeds are normal for a WW2 Medium Tank,
It makes removing/replacing tracks easier if you fit Idler adjusters but if you don't "Fight" your Tank then running it without should not be a problem.
Plastic/ABS Hulls are fine with a plastic body and metal turret as long as some reinforcement is fixed to the side of the hull.
I cut out the battery box to provide more internal space but that is just me,
The advantage of making extra space is that you can fit a wider choice of control boards/receivers/smokers/sound cards all because you can fit much smaller battery's with the same output such as Li-Pos/Li-ions,
Coating the floor of a plastic hull with epoxy resin will add more rigidity.