Hi Dave and welcome to the forum. I think most people who would be better qualified to answer you than I am would probably want to know a little bit more about the hull you are referring to. Specifically what it is made of, coated with etc..etc..

Just as a general approach from my own point of view I have never put a great deal of emphasis on sealing the inside of the hull. I only coat it internally if it needs greater strength or for protection from steam plants etc. When it comes to sealing though the effort all needs to be put into the outside. If you imagine a perfectly internally sealed hull made of wood that has not been properly treated on the outside there will be a possibility of the wood getting wet and either rotting or delaminating with paint peeling etc. Water might not get through to the inside of the boat but the hull can still deteriorate.

My personal take is that sealing the hull completely should be done from the outside. As regards what you use that is very much dependent on what the hull is made of but either two part epoxy coating, such as David's, or water based coating, such as deluxe Materials Eze Kote, with or without glass cloth are all popular. Probably the toughest epoxy is the West system but that is pretty expensive stuff and difficult to sand afterwards.

Generally I use EzeKote to seal the inside and then overpaint with white primer/undercoat. A white interior makes it easy to find things that have dropped off when they shouldn't and looks smart in my view. It's all down to personal preferences though.

Colin

Neil, no need to be sorry…that’s a pretty serious tip you have added to this thread! Ashley

A number of contact adhesive glues also attack and soften moulded plastic hulls.

Colin

Andy. The smoother the hull is before applying epoxy, the better the finish will be.

Sealing the outside of the hull is a must.

Paper tissue and dope was the long-standing combination to finish the outsides of models as it is cheap and what was available at the time.

Glass tissue or cloth is now available. This is very thin, and would add much more strength to the outside rather than paper tissue if using epoxy.

Easy to smooth epoxy using wet’n’dry paper (wet)

Ashley.

Epoxy will take almost any filler. P38 car filler is one of the best in my opinion. Easy to sand, smooth, and can be used as an adhesive…it’s very sticky.

Halfords do a tube of filler paste, acrylic, made for filling fine cracks and dents. Takes a while to set (in this cold).

Ashley

It would be nice to get hold of the filler you mentioned Ashley, Ive found a tube of plaster flier which is pretty handy and sands easily too, It only takes an hour to harden off to sand lightly so its just the ticket for me, ( my shed is 34c-36c at the moment ) so I don't really want to hang around in it for too long.

Ray, it ws supposed to be a pilot cutter, Ive often admired the look of them So i decided this year with this build to buy a fibreglass hull from -? in UK, Easy build I thought, It was expensive but I thought id treat myself, they first quoted 40 pound freight, then sent me a message after i had paid that they couldn't get anyone to deliver at that price but can do for 80 pounds if that's ok, A bit disgusted i cancelled and thought to try an Australian supplier only to find they went out of business. So no plans Ray but loads of pics, So thought why not give it a bash.

Stay warm, best wishes from Queensland

Andy