Nice idea there.. It basically near-doubles your hull but it requires 1-time trap that can be consumed only during defensive purpose. Fair trade.
After all, attackers always repair hull anytime they wish with repair artifacts and also credits while defender has NO way to repair hull off-line and its tough for them to time-repair it during online cuz attacker will click attack too fast.. Trap will serve defender very nicely help to reduce the effect of defender's disadvantage..