Worth bearing in mind that grounding is most likely towards the longitudinal centre point on chassis between wheels. The easiest and cheapest improvement is thus acheived by ensuring seat bolts (particularly front ones) are cut down or substituted for ones absolutely no longer than needed to accommodate nylock nuts. It also means that transmission is more vulnerable than engine sump over speed bumps assuming they are taken at gentle speeds.
Have not had any recent grounding issues on my Roadster despite only 85mm clearance on g/box cross member. I do take these narrrow/steep speed bumps found in supermarket and municipal car parks at an angle though.
