I've added an image of just the
megahex borders that can be overlayed onto any hex map. You'll have to resize it to fit the hexes, obviously, and this is a bit fiddly, but someone may find it useful.
Two examples of maps I've made using gimp:
Both are fairly simple to make, though the second took a lot longer than the first. I use additional layers for GM notes (monster locations, traps, etc.) and hide those when creating the png for roll20.net, which players would see.