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.
Beg your pardon, but what vulnerability ? The thing is , it stayes cloaked for ~ 30 minutes, runs around freely in any system it wants, then leaves on the designated exit without having to use a single sheild battery. I might be watching a different movie, but I don't see the vilnerability in that, since cloak can not be "countered " in any ways.
I shouldn't have to point this out to you... but you can always counter enemy intelligence by having your own intelligence. You can't have it all, but you could always get your own cloaktrans and level the playing field lol