Hmm - just to impart some technical knowledge - the only way C4 would work in this capacity is if the charges were shaped. The very odd remote charges are definitely a 360-degree weapon, and structures have roughly 10 times the armor of a comparable vehicle.All Renegade structures are concrete-foundations except for the GDI barracks - you'd need about a 100 pounds of C4 to do any real damage to a fixed-concrete foundation building.
Another thing - why are timed C4 so much more powerful yet SMALLER than the remotes?