Best way to fix hole in cab seam?

Anybody know what would be the best way to fix this little hole in the back of my xtra cab? I think it was caused by the bed topper which rubs the back of the cab when it goes up which I'm planning on taking off and fixing the hinges. I noticed when I wash the truck the carpeting in that little secret cubby underneath the back seat gets wet which I think is leaking in through that hole. The redneck in me wants to jam some red rtv in there and move on. But what would be the right way? Welding? Epoxy?

 

Tough spot. I would probably scrape as much of the flaky crap away and shoot some automotive seam sealer, then smoosh that in with a finger. The inside is probably sealed as well, but cant hurt.

I used this stuff when I remade my wheel tubs. It comes in a few colors but not red as far as I know but you can mask the truck and immediately shoot it with some red touch up, doesn't need to be dry to be painted.

https://www.napaonline.com/en/p/SEM29392?cid=paidsearch_shopping_dcoe_google

 

The best thing for this spot would be 3M Heavy Drip-Chek Sealer. 5 oz tube is about $20 on Amazon.

 

I would mask anything around the area that you didn't want to get the seam sealer on as well...

 

Do you think

$30 3m 5200 (06504) Permanent Bonding and Sealing for Boats and RVs Above and Below the Waterline Waterproof Repair, Black, 10 fl oz Cartridge

3m 5200 would work as well? It's a pretty heavy duty marine sealant that I already have a few tubes of already

 

That should work fine unless it is made for fIberglass only.

 

This, it likes to run and it is STICKY!!!

Be aware it is light green in color. It'll take paint well but it needs to dry completely. It does not get hard but remains pliable. It does not sand well so any sanding or bodywork around where you are applying it needs to be done first.