I recently used a giant dungeon for HARP, which has similar issues, just made sure to spread the dangerous monsters out a bit, and they set up a base to retreat back to, which they did whenever the PP ran low. . .the one upside of HARP is the fact the ranger and the priest could both heal, so it wasn't one of those situations where "Oh crap the priest took a hit in the head, we're screwed."
I've done RM dungeon crawls as a PC and a GM, and I think my experiences there allowed the HARP game to work. . .I think the key elements are:
1) Watch the pile-in effects: RM combat is ill suited to another 5 goblins showing up every round for 10 rounds.
2) Keep the monsters separated: Partially due to 1, and also so that the PCs don't flee from monster 1 into monster 2.
3) If it's anything like the scale of a D&D dungeon, have the PCs know that they likely will need to hole up and rest a few times, rather than clear the whole in one run.
4) Smart/organized dungeons, rather than ones with a lot of individual, separate encounters (like the slaver modules or the giants of D&D) will likely overwhelm the PCs unless they intend to be very sneaky, or have a lot of backup handy, or are WAY over the usual level. (Like five to seven 50th level PCs might be able to approach something like G1-3 the way a D&D party would)
4) Make sure to have two healer types, or a healer and at least one healing item (held by a character other than the healer).