Why would you care about weight if you don't intend to move it much?
The price is much more important.

A container full of missiles is expensive enough to actually force an army to use it only at high value targets - and to avoid its loss.
It mus not be left behind, even if broken communications or other factors prevent timely use of the missiles before their position get overrun.

It makes sense to think of this as a container on a truck - a mobile launcher.