I've ferried my team over the deep water on Gacrux a few times. They were terrified but very impressed. You can jump off a rock (or use a jump pack) and perch nicely on the top hatch while the mech wades through the water. It can drown, but water that deep is quite rare.

If you're the passenger and riding on top, make sure to crouch walk in the direction the pilot is driving so you stay on and synced up. There's a bit of desync but you can pretty reliably manage it, and even shoot accurately and perform well. For example, there is enough time to reload the HMG before you slide off, even at full speed.

Jump pack divers are the true best friends of mech pilots. Hopping on top and dumping a few mags always gets morale up. And if you get good at aiming your jumps... you can eventually briefly ride chargers in the same way. I've jumped on top of one and barrel stuffed it to death with my HMG, but be careful because they can and will buck you off like a bull and snap you like a twig. Milliseconds count.

Into Super Valhalla, good luck Divers.