We use POR 15. But a pump style pesticide sprayer from Lowes, Home Depot. Fill it with some POR 15 stick the nozzle in and drizzle it in. For a deck lid I'd remove it 1st. Be prepared for some to ooze out the seams. I do firewalls, doors, hoods, around the 1/4 panel lips. Leave doors open. We generally do this before painting. so when it runs out you can wipe. It STICKS WELL.and seals. Dries like concrete. We have stuff running around for 15 years or more on this method with no signs of rust thru. When you're done. Thru the sprayer away.
Doug