I personally find no issue with transports being reused as surveillance vessels, their overall vulnerability seems to be a fair tradeoff for their capabilities to stay cloaked for longer than usual, if we compare them to caps. While I find the terms "perma-cloak ship" and "cloaking for hours" qute exaggerated, I agree that 15-20 minutes of maximal cloak time could be toned down a bit. I could imagine a Cloaking Device Mk4 created for use over 1,5k-2k cargo (idk what's the upper cargo limit for caps), and then said device could have different commodity consumption rates to balance out specifically transports.