We have two steelies. I agree with all that has been said above.
One is traditional build, the other has only stringer. I like the stringer only design because it eliminates places for water
to hide and create rust.
I've see some boats with lots of fairing (bondo) that look great, but that proves nothing. I put a big dent in one boat a while ago, and filled it with bondo, just for looks. A glass boat would likely have had the hull deck
Our smaller boat has NO bondo, but is very fair. Yet I will have to do some plating on her before she goes in the water
. This boat is 10gage (3mm?) steel
, which is fine for that length. ....photo below....
I have seen boats up to 48 foot in 10gage, but not for me.
1989 Custom cruising ketch Sail Boat For Sale - www.yachtworld.com
But even our 44 has two spots where there were persistent leaks
under a sink or refer that were not attended to and that caused very localized heavy rusting that required plate, that's why I don't trust ultra sound, the rust can be VERY localized.
If you can try to get a boat NOT constructed by an armature. Not that they are bad, but at least look at a couple of pro jobs so you can see the difference. We once walked out on a nice aluminum
boat because welds were not up to snuff. I could only tell by comparing with a couple of pro builds.
Here is a good resource...
Metal boat maintenance-A do it yourself guide by Scott Fratcher (eBook) - Lulu