Hi and welcome to YT! Congrats on your little one. I have both of mine trained to use pads and outside. I have a pad inside in their pen area and in hubby's garage for those nasty weather days--they can still "go out".
Sounds like you are doing the right thing with your little guy. I would maybe try putting down several pads together, to give him a bigger space, he might just hit the pad from time to time.
Eventually phase down the amount of pads.
Gating him off is a really good start. Have you considered an expen? It's the same concept but in a smaller area. You can have all his things in here and put a plastic shower curtain under it and line pads around. It's pretty much the same as you doing but in a more confined area.
Because you are gone at long stretches of time, you will have to work a bit harder when you are home. Get to know the signs of when he has to potty and take him right over to the pad. Once he starts to go, pick a phrase and use it only for that purpose. When he does go, praise and praise more or treat him. One day, it will click and continue to praise and treat. lol, if he's anything like mine, he'll learn really quickly to pee on the pad, run over for his treat and then go back and poo on the pad and run back for another treat. lol The best thing that I could recommend is to have patience. It will happen. I think that mine kinda got the idea at about month after we started...but I was at home with them full time, it may take a little longer but it will happen.
Here is a picture of our expen, I now have only their beds and blankets and a pad in it but mine are 3 and 4 years old and they only sleep in their at night. Not sure if you can find them where you are but they are on line too.