Well, I don't know anything about playing on a PSP, but to be clear, I'm talking about playing the original PS1 WC3 discs on a 60GB PS3. And the crashes I have on the carrier aren't random; they occur every time. The one's in the destroy capship missiles/rescue Flint missions are unpredictable though.
Anyways, using the memory card adapter and a PS1 memory card, I took my save file to my friend's 80GB PS3 and tried it there. Same "chunk not found" and "bus errors." I bet you'd get the same issues on a PS3 slim since I believe the PS1 emulation is done through software so should be universal across all PS3 configurations. However, after trying my save on his PS2, I had no issues, thus I am prepared to conclude that the problem is with the PS3's PS1 emulation. As a poster has mentioned, the PS1 port was glitchy and probably does not conform to PS1 specs, but maybe Sony can make their emulation more robust.
Anyways, I've brought back the save file that passes this mission back to my PS3 and will try to continue the game from there. I'll post if I continue to encounter errors.