I had 17 individual 'lag screws' holding my '73 Boler
shell to the frame. A few had rusted through, others were loose; but, most were reasonably firm. I merely searched along the entire floor, guessing just where the frame rail would be located beneath the floor, and found all of them. They were all similarly spaced; so, once the obvious ones were found, the search led me 'under' some interior items like the water tank (which required removal) and, into the very narrow area between the wheel well and the shore-side panel of the rear dinette/bed and cupboard. Once I started lifting the shell, the remaining screws became more obvious. After sand blasting and repainting the frame, a complete set of new 'similar' lag screws, with supporting wide 'fender' washers, were used to replace the original lag-screws. I chose to add four new 3 1/8 in. SS 'bolts' inserted through newly placed angle-iron braces I had welded to the frame near the four corners of the shell/frame contact. I now believe I have a very securely mounted Boler
shell to the frame.