Weapon and ammo in separate locked containers when stored in a vehicle. No trunk? Put one in a locked container behind the seat, the other in the glove box if it is keyed lock. If not, lock it up in a container and put it in the glove box. Next, a weapon in a locked vehicle is a no no.....especially in MA.
Lots of questions regarding this topic. I believe it is actually illegal to leave your weapon unattended in said vehicle/s. I still cannot find where it states this word for word though. And, if you ask a LEO they'll give you different answers. My suggestion is, do not leave it unattended as others have said.
If you do a search on this, I believe I asked the same question some years back and someone actually did find something on it. It was in this section......try maybe at least 2-3 yrs ago looking for my user name sambo42xa.
(All the above are MY opinions/suggestions ONLY....AND, I like to bust ball's, it's called having a sense of humor. In other words, no intent to offend anyone, so get over it)