I reused the exhaust tube, in fact it's glassed in and you don't have to remove it, just around it. The thru-hulls I repalced as they were plastic and brittle therefore they broke. Since the transom was isolated area to paint. I chose to do it from the outside, because it was easier to get to. I found that the water on my starboard side went down to the center line. You can't get to it all from the inside. The rot will not be uniform, some places will be completely rotted others just saturated. This creates problems if you are trying to save the old skin. In some places it is wet but still adhered to the skin, which cracks when you remove it. I found it easier to cut out 3x3 sections with a cirlcular saw, the expand the hole until I hit dry core. Some of the core may look dry but if you start chiseling you find that water seeps out.Working from inside the cabin will be difficult. When you are working over head, It's hard to keep the core in place without a lot of bracing and it's harder to get it to adhere evenly. Plus there no way around it it's a messy job, No matter how careful you are resin ends up every where. I plan on working my deck from the topside, but I need to repaint anyway.