And when the Mortar is not installed, it can carry 2.5 tons of cargo at 9/14. (what would be the price of this version, no MM+ammo and just cargo instead?)
I could see these trucks being used by a variety of militia units, with just a small maintenance outpost + crane being used to mount Mortar systems when needed. If you could reduce a Lift Hoist to 2.5 tons you could make one of these trucks into a decent tow truck as well. 2.5 tons/3 tons = 83.33%, so instead of being able to lift 2.5 tons, it can lift just over 2 tons which is enough to put the Mech Mortar in place with the technicians attack the MM properly. Turns any tow truck + transportation unit into a potential combat unit as they can just drive over and start attaching the mortars. If a truck gets destroyed or just breaks down en-route, there are plenty more.
This is a very simple and effective design, great for causing headaches to enemy bases. Just drive one of these up near the enemy base (but behind cover), fire off a dozen shots, then leave. The cost of the half ton of ammo is almost equal to the truck itself, so even if the truck is destroyed you likely got your money's worth.