Well, I beat it. 4 Sweet Potatoes (my new favorite food), along with Chaos Shields (upgraded with a Pretty Carapace, 2 Insect Carapace, and Ghost Hoods to give them 100% to Paralysis/Poison/Seal) and Ruby Rings (50% Fire Damage Resistance) on both myself and Forte got me through with relatively little problem. It did require too much food, in my opinion, and it took too long, but I did it. I got up to the boss, unlocked the teleport point, and then went home or I wouldn't have made it back before 1:00 AM (and if you don't sleep before 1:00, you get no sleep skill boost). And that was starting from the first teleport point, not even the beginning of the dungeon.
Also, skipping rooms is a bad idea, Neo. Several of those rooms you just run through have items in them. After the first save point, go up and to the left. You'll be in a long room with a monster generator at the end. Past that is a heat room filled with Fire Elementals. As long as you're in there, you'll take about 5 HP damage a second, but that's really nothing. Kill all the Fire Elementals, and a chest will spawn containing a magic spell (I think it's the one which shoots Wind Crescents, but I'm not sure.). There are rooms like this in the sub-dungeon of the forest too, and that's only one of the ones in the Fire Cave.