What do you recommend?

I tried some 3M 5200 marine caulk and it seems to work very well. They make a quick dry 5200 also. The regular 5200 takes a long time to set up. The product is for the marine environment and stays flexible. Also a recommendation about using masking tape along the joints. This keeps the caulk confined to a narrow area and an neater job. After you get done you just pull off the tape. I've seen some folks caulk and use their finger to smooth it out. This leaves a very wide unprofessional looking job. Use masking tape!