I sympathise with you. My dh has periods of frequent travel, usually only for a couple of nights at a time, but sometimes for a week or a fortnight. On the whole, I would say I am confident being alone, but for one thing that overshadows my life: a phobia of vomit. I know it sounds crazy but when dh is away, I am terrified one of the children will be sick and I will have to deal with it alone. It is even crazier given that, even when dh is here, I am always the one to deal with any mess.
Anyway, at the moment, dh is rarely away and my youngest is now 12 so probably being alone with them would not be such an issue for me now.
The above may sound a bit irrelevant to you but I told you it to show that I understand where you are coming from. Dh often did not tell me in advance about his travel plans, but for a specific reason and I am wondering if your dh is not telling you for the same reason: he doesn't want you getting worked up about your forthcoming time alone? I know from the moment I knew a trip was in the offing I would feel anxious and depressed. Sometimes the time he was away was actually less stressful than the build up to the trip. Mind your dh be sparing you the anxiety?
I rarely knew where my dh was going either. It didn't really matter to me as I could always contact him on his mobile. Obviously, if he was going to another continent it was a bit more of a thing, but if he was somewhere in Europe, it didn't really matter where he was.
I didn't have the worry you have about who he was with as his trips were usually solo affairs or with one other male colleague. Do you have any reason to distrust your dh with other women? If he works with them at home, is there any difference to working with them away?
Re contact, I have to say I think your dh is slacking a bit. My dh, on the whole, would ring every night he was away, although I have to admit his calls weren't always welcome by me.
But then, my dh was usually bored in the evenings, in a hotel room on his own. Apart from being taken out for meals, he didn't have much else to do. And yes, he would always ring if there was a specific ongoing concern, eg a child ill.
I don't think it is unreasonable for you to want to know what you want to know and for your dh to make some regular contact with you. I do slightly wonder though why it matters so much to you where he is and who he is with.