Tightening V2 tower bolts

I noticed this last weekend the bolts on my V2 tower have some movement when I was lowering it to put it away in the garage. The bolts look like a huge phillips screw head. I found the largest slotted screwdriver I could find, along with a vicegrip on the screwdriver and tightened them as best I could. Is there a special tool for this type of bolt head? A typical phillips screwdriver head, even the largest I could find, isnt enough to tighten these as much as I would like. What is everybody else using to tighten these?

I also noticed, when I have the tower lowered, I can move the base (where it attaches to the boat gunnels) back and forth a little bit. Seems crazy something this large and carries a heavy load, would move even a little bit.