Since the challenge is more about survival rather than succeeding at anything, if I'm running any of the heavy armor classes, I'm most likely running something like Byr's. As cleric, for instance, I'd focus on AC, wait until first two combats are over, heal up, wait for combat to end, heal up, etc.
There are better commons than there used to be, but even those are really to help a full party survive until a room 7 slaughter. Outside of a paladin one-shot kill on something, is a devil drake a devil?, one adventurer just outputs so little damage.
Also, solo play is not 5 rounds of combat. In my last solo run, Dalin rm2 was 9 rounds, rm3 was 7 rounds, rm4 of 5ABC actually goes superfast on solo, rm5 died. In my much more successful solo run on 5B, Dalin rm2 was 17 rounds, rm4 was 4 rounds, rm5 was 3 rounds as I finally rolled a 20 with Ava's, rm7 would have been an extremely long slog if my build worked the way I had planned it to work or I would have rolled a ton of 1's on saves to get hitpointed before inevitable victory.