Yep, I can help! I am also chronically hypoglycemic and the "trick" for me is fueling early and fueling consistently. I use Tailwind or the on-course Powerade in my water bottle, and I take a gel (100 calories) every 45 minutes. The fuel every 45 minutes is the really crucial part, but I found that the little extra glucose in my fluids helped in the latter parts of the marathon. I also eat breakfast before all races - around 2:30am - and have a granola bar about an hour before I start. I bring at least one more gel than I should need, just in case of a delayed start or lost gel. The one time I had a huge crash was when I failed to take a gel on time: I was at mile 12 of a half and thought I'd just wait until I finished. Nope. Big mistake. I have my running app programmed to alert me to fuel every 45 minutes and I now do it when I get the alert, no matter where I am in the race!
My Dopey training simulations have topped out at a long run around 20-22 and that was all I needed. By making my fueling time-based instead of distance-based, I stay on top of it, no matter how many miles or how long it takes me to complete them.