It doesn't matter how we do it, we need armour capable of shrugging off long-range rifle shots, and preferably also surviving at medium-range. Ideally, the armour would come in the form of a vehicle that further reduces their rifle advantage by letting us easily close to medium range. Even more ideally, the vehicle would be amphibious, to help on C2, and generally all-terrain-capable, to help on any other planet we fight on.
I'm not sure a one-man vehicle like a bike is exactly what we want, but it would stand a better chance of being 1 CU. I don't think being atmosphere sealed is a good idea (would make getting in and out too complicated). How does this look:
Gyrinos (Tadpole): The Gyrinos is a relatively simple vehicle. The rounded exterior is lightly armoured, capable of shrugging off small arms fire at long-medium range. It has a single wheel in front, and tracks in back, to provide mobility on all terrain. Time permitting, attachable floats and propellers will be designed to allow the Gyrinos to be modified to travel over water as well.
Internally, the Gyrinos seats a single soldier in a X112 space suit, who enters via a large door on the side. A second soldier can hang on to the back of the vehicle, in a somewhat less comfortable manner. For firepower, two Jormungandr Bolters are integrated into the vehicle on forwards-facing mounts. The Gyrinos is battery-powered, and has deployable solar panels to recharge. It can travel at top speed for about an hour, or 'cruise' at a lower speed with solar panels deployed indefinitely.
Target distribution is one per ten-twenty soldiers, with squads of Gyrinosi travelling ahead of the infantry to clear out snipers and capture strategic locations, with the infantry serving to clean up behind them, or hold defensive positions.
A crucial design requirement is that the vehicle does not take up too much space in a transport (1 CU or less).