P.E.- Or why isn't there P.E. for Papermodels?

The Quick answer is sales VOLUME.

Plastic kits are sold by the 10's of 1,000's, paper models.... aren't, so there is a market for kit-specific PE & resin.

I tend to re-scale the card kits I have built to 1/48th scale, so even then, I wouldn't be in the market for the card-kit specific PE, etc., & you could re-scale your floaty-boat things to a common scale?

Some of the Polish card kits are available with Laser cut (still card, mostly) frames & Vacform Canopies, but I don't know about ships.

I suggest you look up the Model Shipwright sites, & search for WEM especially, as there are generic PE sets for railings & stairs in the various common scales.

Actually, there are loads of detail sets -- both PE and laser-cut -- primarily for paper model ships. They're harder to find, however, because they're virtually all done by European manufacturers for that market. Check places like the Paper Modelers Forum (papermodelers.com) and vendor sites like Fentens (which I believe is papermodel.com.au) -- you may be surprised how much is available.

There are also 'generic' detail sets, mainly railings and ladders, in most of the common paper ship scales.

I used an HMV-made P-E set on their 1/250 USS Maine which I built last year. I might have been able to scratch or source things like lifeboat frames and railings...but having made-for-the-model rigging/ ratlines was a huge convenience, worth the price of the set for those alone.

Cheers