Advice on less fertile days please!

So my boyfriend and I are TTC but there's one problem....HE'S A TRUCK DRIVER so he's gone for weeks at a time and usually not here on what my chart states as my most fertile days (27%-33%). The days he will be here are the ones that I have a 3% chance on or my period days (of course lol). This wouldn't normally be an issue because I know I am fertile but he has slow swimmers. I've seen the posts on maca root capsules and raspberry tea. Do they really help? Is there any other advice that would be helpful? Maybe something he can do to increase chances from his end? Thank you!