to beat the Rhen Var mission, do only oen thing the mission breifing says: fight the enmey in the ice caves.
select the clone trooper , and start in the ice caves. got near the exit of the cave nearest enemy territroy, and stop by the ice pillar. get down into a crawl position just so that your gun has the perfect shooting position but you can't be hit by most enemy fire. shoot down soem enemies, thrwo grenades at clusters of droids that coem to the cave entrance, and hoept hat soem engineers will drop health/ammo packs for you so you don't have to go bakc to the main cave chambe rto heal and reload over and over again.
with drodideka simply get out of theyir lien of fire and wait for their sheilds to go down after beign sustianed for too logn fo your own guys knockign otut heir sheidls. don't waste blster ammo or grenades agaisnmt their sheilds, jsut wait. occaisally soem droids will break through, and that is when you most need your grenades. make sure freidnly fire is off. it's incredibly annyogint o accidentally shoot down and blow up twenty of your own guys when jsut trying to blow up soem droids.