I personally go with any model paint thinner for enamels, doesnt matter if its Humbrol, Revel or something else - it needs to be for enamels. Other folks may give other advise though. Also be sure not to rub it in hard, just spread it over. So basically paint it panzer gray and after that wight wash it with very thinned white paint. You will have to come up with a ratio, lets say 2-3 drops of paint and about 10-15 ml of thiner and see how it goes. you can add either if the color is getting too thick or thin. What wight wash will do is break the uniformity of the gray - give it a bit of unevenness. When doing this you will notice how the thinned paint tends to accumulate in recessed areas such as pannel lines. When you do a black wash later - do it mostly over such areas and it will make shadows and pannel lines stand out. If you are not sure, first test on a different surface - for example the bottom of the tank or a rear mud flap, something you can quickly fix or wont be visible.

P.S. Ideally let each paint coat dry until the next day before you do something else.
P.P.S. If it looks bad, let it wait until tomorrow and its dryed out before you panic - usually it looks better when nicely dryed. Scrutinise it then, maybe you ll like or maybe you ll want to fix it. Thats what happened with my wightwash, I paniced a few hours after doing it and started removing the paint with thinner. After removing half of the paint I got really pissed off and went to bed. In the morning however, the other half had dryed out and it was no longer sticky. Now I have to do the other half again.

This my first RC tank also, so Im a bit worried about how its comming along as well. I ll make some photos tomorrow.
Btw, the hoses of the feifel filters of my tank were very glossy, I gave them a thorough witewash and they look much better now. Also tryed the HL decals but they are awfull and removed them immediately, ordered some proper ones today.

P.P.P.S. I seem to have spelled the color white in quite a few wrong ways in my posts [&:]