Since you mentioned wanting to take advantage of the 3x exp stay, I assume you also wouldn't mind saving up exp. For those reasons, I shall suggest the method I used because it not only gives acceptable exp, but also very good amount of gil. I cannot say this is the "best" way to farm gil, but I found it extremely lucrative.
First, if you also wish to farm up some exp, you will want to at least activate a food with 100% exp gain while doing this method. There are other things you should also do, but since your question isn't about farming exp I won't go into those.
For the gil farming specifically, You will want to go to the Verinas mart outside of Ravatogh mountain. The tipster there will have a hunt named "Verinas Mart Under Threat". This hunt has you kill 7 wyverns that are just north of the mart.
Using the Ring of Luci special ability "Death", you can one shot each of these wyverns, making the entire fight take roughly 20 or 30 seconds or so. Each dead wyvern drops a wyvern tail. By the end of the fight you should receive
7 Wyvern tails
Now return to the mart by either walking (it isn't far), teleporting back to your car if you parked it at the mart, or return to your last rest area if you slept at the mart before you started racking up exp. DO NOT SLEEP AT THE MART IF YOU ALREADY HAVE EXP SAVED UP)
This hunt is repeatable and I believe it gives 1950gil each turn in, or thereabouts. This in itself isn't significant, but it does add up when you can complete the hunt very quickly. The payout however is form the wyvern tails. Each tail sells for 1600 or 1650 gil each. So your banking about 11.5k gil each hunt run.
I farmed this hunt for about an hour, for both exp and gil and walked away with over 300k gil. Just make sure you sell off the tails when you reach 99, it is easy to fail to notice you have hit the inventory cap and you will loose tails.
Farm the Verinas Mart Under Threat hunt for roughly 14k gil each run. Each run takes about 1-2 minutes from start to finish.