i was thinking trench coat older gas mask but what for pants and under shirt
If you have to crawl inside a tank, your gear should be as simple and streamlined as possible. You don't want your fancy clothes to get caught in some sharp angle or moving part when the tank is hit and you have to get out quickly; british had the idea to have an handle sewn into their tank uniforms to help dragging a wounded comrade outside the tank. Headgear shouldn't be too clumsy too. You don't need heavy boots as you are not going to march your way into enemy territory like ordinary troopers. A retro alternative to gasmask may be a chainmail mask.
i think that most tankers wore a simple set of coveralls, especially green, olive, or khaki. -and i don't think i've ever seen one wearing a trench coat; i think their coats were pretty short.
Trench coat must be rather short one, and I'd suggest googles instead of gas mas. Corcoran Tanker boots look great. Pants- any 'cargo" type would do, I believe, preferable green, grey, haki, black, brown or even blue. The most important part - overall look must be a mix between "soldier" and "mechanic".
Good suggestions from Leviathan, by the way.
If you prefer to go for WWI style, here's a fine example from France:
This regiment was initially equipped with chars "Schneider" (Schneider tanks) and later on with chars "Renault FT-17" (Renault FT tanks).
The regiment saw service on the Western Front and later in the Crimea, fighting the Bolsheviks.
Photographer: Delorme, 28 Rue Moyenne, Bourges
(by Dutchie1953 @ Flickr)
For style you cant beat the German's Panzerwaffe uniforms,look up Micheal Wittman,an SS tank ace. baggy black trousers with short black jacket..which is what i wear pretty much all the time if im not at work.i wear a pair of 40inch waist(i take a 32') very Black jeans with large double buckle belt and 'blouse' the bottoms of the jeans with elastic bands over tall boots....the soviet tank helmets look very good 2...they dont seem to have ever changed the style of them since the 30's and i got one awhile ago for only £25.
de Fink i like your idea it looks like what i was going for too