Congrats on your new purchase you must be very pleased and looking fwd to the trip. Photo 13 here
australyachts.com/#clubman8 shows the fore cabin view of the 3 channels.
The internal 100x120 patch on each could work - how long are those channels and what is their maximum width and depth? Unfortunate that the cracking has been left to propagate past their fwd end into the deck proper.
To do it right it would appear that the on top of the deck cracks need to be carefully gouged out with a suitable fine hand tool or 1mm drill bit, acetone cleaned and epoxy glue filled. Sand and apply neat biax or triax cloth layer/s with epoxy resin in the channel from above, going out say 20mm laterally beyond the edges and extending say 40mm forward beyond the existing crack ends. Sand and fair, 2 pack poly paint to finish off. 2 colours needed - Inspirations Paints will tint Northane to the deck colour.
Then apply the 2 layers of biax or triax with epoxy resin under the deck - say a circular patch of diameter the length of the channels and crack extent plus 50mm. Getting the carpet and glue off a necessary pain as you say. If (as expected) the cracks are all the way through to underneath then gouge out and epoxy glue fill them also before applying the glass laminates.
Good biax and triax supplier here but the small quantities you need might be difficult to get.
www.colan.com.au/compositereinforcement/stitched/triaxial.htmlWould not use carbon fibre double bias - see the Colan website for it - as you allude to this laminate will be a lot different to the probable E or S glass of the original laminate. The main difference being stiffness - so the carbon fibre patch will create a stiffness mis-match to the original laminate and the original laminate won't take it's share of the membrane and bending stresses. Stiffness being the initial slope of the material stress-strain curve. Brittleness is the amount of elongation to final fracture - lower elongation means higher brittleness - and carbon fibre will be more brittle than E and S glass as you say. But the stiffness mis-match is the issue.
The last person who posted at the below link in 2020 might have some comments?
www.seabreeze.com.au/forums/Sailing/General/Austral-Clubman-8--leaks-in-keel-box?page=1