im having trouble cs'ing on rumble.

Electro-Harpoon is pretty much your main CSing ability since it lets you safely farm from a distance and deals similar damage to your basic attacks at rank 1.

When CSing under tower, if needed you can use a tick or two of Flamespitter to lower the health of minions enough that you can kill them with one basic attack after they take one or two tower shots. Improperly using this can result in missed CS, so it takes some practice. Make sure to turn away from minions after you lower them far enough so Flamespitter stops hitting them.

If you are having difficulty CSing under tower, it may be a good idea to overheat (preferably with your shield for protection). Your passive makes up for your lack of AD when last hitting under tower. However, this does leave you vulnerable so be careful when you do it.

Also, unrelated by I noticed that you don't seem to upgrade your trinket very often. It is extremely cost efficient and vision is one of the most important aspects of the game, so I'd recommend that you upgrade it ASAP pretty much every game.

Really? I can't recall ever having problems with him. His Q takes out the whole wave pretty much by itself and you can farm from distance with E.