2.6m dingy hull extension, fiberglass rib boat

I have a 2.6m fiberglass hull inflatable boat collecting dust as I have upgraded to a 3.1m of the same brand.
I'd like to remove the tubes, split the hull, fiberglass in a 2' extension, remake the tubes with better fabric, and put it all back together. I've grown my competency and confidence for this slowly with several projects over the past 2 years. My end goal is being able to offer tube remakes and repairs for my island.

I'm basically turning the smaller RIB into the bigger RIB. I already have several meters of Orca Hypalon fabric and the appropriate glue, tools, and workspace. I have a general idea of the work ahead, but I'd like to hear your details about making the mold. I have the bigger boat on hand, so I'll be able to use that for reference.

My plan is to line up the two hulls upside down and find the straightest section. Tape it out, get the lines nice and straight, then wax it. Should be able to make a mold in the shape of a tent. Two rectangles joined together at an angle. Most likely will have the strakes in the shape also. Laying up the mold into the new hull sounds easy, sort of like a transom extension.

Am I missing anything there? Any issues creating a partial mold from a hull? Is there a better approach to getting the shape I need?

Tubes are straight for a large portion, so adding onto the template shouldn't be overly complex when transferring to new fabric.

I've attached dimensional drawings of both RIBs. You can see how similar they are. The tube diameter increases with the longer boat from 15" to 16.5". Ideally I'd increase diameter of the tubes accordingly, but as this is mostly an educational project, that detail can slide.

Thanks for reading. Appreciate your input