There is a little exploit with the The Dapper Sapper Achievement, which will make it very easy and quickly to plan the 100 Seaforium charges for this achievement.
Plant 100 Seaforium charges which successfully damage a wall
This suggest that it is supposed to be used on the walls before they are broken. However, it’s currently bugged. So you get even credit for it, if you place it near a broken wall (gate).
Knowing that, you can just “bomb” down the broken wall until you have all 100. As there are two walls/gates, it’s best to take the gate where no other allies are and after 1-2 min usually no one is anymore at the strand. This means, you can simply pick up the Seaforium (wordplay on C4 (pronounced similar to sea for) charge and place it and repeat. This way it’s possible to plant 8-14 charges/battle depending how fast your faction needs to win the round.
Update: It also works with Explosive Expert Achievement