Marathon fuelling for a bigger man.

Hi all, I have my first marathon coming up and I want to fuel correctly especially as I’m a bit bigger (120kg-115kg on a good day). I have previously run 2 Half Marathon races last year but kinda raw dogged on fuelling during the race and just hit some oats for breakfast and a couple bananas so I naturally gassed out. I just ran my final long run (Half Marathon 2:05) for which I had electrolytes and 4 gels but I still started to fall away during the last 3.5-4kms, I have also run 32km but that was strictly conversational pace with a 3:35 finish so my 6 gels felt adequate. Has anyone here run a marathon at this weight in 4hr 30-45mins and what was your fuelling structure?