When sealing a semi-permanent hatch such as a gas tank hatch or the like, try placing 80lb - 100lb monofilament fishing line around the innermost edge of the hatch lip (edge closest to the center of the opening) using small pieces of tape (duck tape works great, but small pieces!) to hold the line in place. Leave approximately 10" to 12" of monofilament at each end of your "loop" around the hatch lip so that you can grab each end and pull up on the line to release the sealant when you need to access the compartment. You'll need to figure out how and where to store these "grab ends" of the monofilament as you won't want them just flopping around the deck/ hatch area until needed. Then apply your 3M 5200 sealant (or whatever your preferable sealant is) over the monofilament removing each small piece of tape during the process. Then lay your hatch cover in place. When it's time to remove the hatch for needed maintenance or repairs, remove the screws (if used to hold the hatch down as well), grab the ends of the monofilament, - - and pull! The monofilament will cut through the sealant (if done properly to begin with!!!) and the job of releasing the old sealant will be fast and easy. The sealant will most likely remain attached to the hatch cover, but it will be far easier to remove once the hatch cover is out.
Submitted by: Tim Harschutz, Captain - Old Salt (1985 24' CC G-W "Fisherman") Virginia Beach, VA