All methods work fine, pouring resin in a hull gap with no cloth will water tight the hull, but it will cost you extra weight and won't add much strength that's why we normally add cloth to the resin to create a Strong casting.
Adding cloth will do the same thing watertight the hull and add strength, but it will take a bit more work to get the cloth into all the gaps and no air bubbles where water might get trapped into should you not seal the hull properly.
P38 (body filler) around any gaps, planking gaps etc and sanded down will help seal a leaky hull. you could use an equivalent wood filler, but this will require a sealed finish/ sanding sealer or a paint as P38 can be porous and wood fillers on a similar wavelength.
I use West system epoxy or the fasglas (halfords cheappy tins) they do work really well, if im glassing up larger areas i will use the west systems expoxy as i can get up to 2 hours work time using their slow cure mix, but mostly for hull repairs and sealing i do swear by the halfords fasglas cheap 10 min setting time epoxy.
Not sure if that helps maybe...
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