What I did last year with my then 10 month old was bring down our pack and play. Its one of the newer ones with wheels on the end so I could roll it down to the pool/beach, set it up and put my munchkin inside with some toys. He loved it and with the winds and the shade he would take his nap in there no problem too. The only problem is he loves to watch people so we had to hide him from the view of the walkways or he would never take a nap! Then when I was done I could bring the pack and play back upstairs and set it up for night time. It sounds like a pain in the toosh to do all that but it actually wasn't too bad and the benefits completely outweighed the minor aggravation. Your 18 month old may be to big for the pack and play but I figured I would throw out the idea to anyone perusing the board.