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You will definitely rely on a BM support gem for Ground Slam, you haven't got any mana management and with a big part of your mana pool reserved there is simply no other option.

Your build itself looks quite decent already there are just a few things I'd like to point out.
You should definitely take a look at "Unwavering Stance" and "Iron Reflexes" both are incredibly good keystones for a melee marauder.
Stance is in my opinion a must have, not being able to get stunned will save your ass in end game content a lot, and the sacrifice of not being able to evade attacks isn't that big.
Especially not when IR is taken wich will convert your evasion to armor thus providing a great boost to your defensive capabilities.

I'd also recommend getting "heart of the gladiator" right in the marauder starting area it's a really good node and since you're close to it anyways there isn't really a reason to not pick it up.

you have absolutely no armor or resists. good luck.