A small utility bulb can be utilized by running it up into the various compartments of your boat in a dark room where you can often find signs of impending trouble where too much light is coming through. You may also wish to pressure test your bulkheads, seams, and compartments once a year or every other year, especially with older boats. Simply fill the cockpit with water, ensuring the hull is properly supported, and visually inspect adjacent compartments for leakage. You can also fill the compartments with water and check other areas with the kayak right side up and then down. I use air pressure with a special hatch and valve, and cover the boat with soapy water.
Bubbles appear where a problem exists.
I wouldn't do the air test with a lightweight lay-up. Small Repairs Dings and scratches are all part of the fun, but the cumulative total over the years is irksome. Deep scratches or missing chunks of gel-coat do require your attention. Stores that sell fiberglass materials can set you up with all the necessary stuff, and most are more than delighted to explain to customers, the proper and safe use of resins, fillers and hardeners. Preparation is key, so don't expect to rush through the job, though total repair time is minimal once through the learning curve.