Are you able to carry in Arkansas in your vehicle? I would assume the answer would be yes since you say your are a CHCL holder. Therefore, you are able to carry your gun on you in your vehicle. Your question specifically asks if you can leave it in your vehicle.
I totally get why you would want to do this since your work building disallows the carrying of it. The question then remains, how do you store it in your vehicle. I will answer it with another question. Do you want it stolen? I'm sure the answer is no. Therefore, don't store it in the cabin, but store it in the trunk as if you were doing interstate travel through some of the more liberally minded states (ammo separate).
I'm not an expert on Arkansas law, but if there is no law on something, then it is legal to do so. Read your section on firearm laws form Arkansas and if there is no mention about locking your firearm in your vehicle while you are away, then it is legal to do so, since there is no law against it.