Where did you lose? It really pays to overtrain in insane mode. It's a bit easier with the GM auto trainer, although I don't know if that's still out in userscripts.
First time, I got careless and lost in Terror mountain... Second time, I didn't use a healing potion at the right time, while battling zombom ==;
It gets a lot easier once you get Velm, but until then I would suggest overtraining until you get little to no experience from monsters, and keep your potion levels high. If training manually, it doesn't hurt to turn off hunting mode. The extra steps you obtain will heal a few hit points. As for bosses, always keep your hp above a certain level. That level should be above the max damage that they can deal. But yeah, it seems you know what you're doing. The prize at the end may be worth it...if you get BoD or WoR.