Help with house training..

I would train to a litter box (cheaper in the long run than pads and more distinguishable from other places for the dog) and encourage him to both pee and poop in the box, but also to go outside on leash.

This way he can be left home alone without issues, and you won't have to take him out in inclement weather.... but on a travel day you can walk him during a rest stop and he will know just what to do.