If the hull is screwed together, you can remove panels, put a bead of 4200 or 5200 on the mating surface and then screw the panel back on. Basically take the dinghy apart and seal the seams as you reassemble it.

If you have chine strips along the seams, you can glass over the seams on the inside or fillet the seams with thickened epoxy. To glass over the seams I would cut strips of mat, wet them out on a piece of cardboard and lay them in. Use a chip brush to work the mat around the chine strips and an air roller if you want to get fancy about getting air out. Filleting the seams involves mixing up epoxy thickened to peanut butter consistency with 403 microfibers and laying it into the seams. Use a rounded piece of plastic or your thumb to smooth the putty into the seams. Either methos will seal and strengthen the dinghy