if your worried....
Why not make a cradle or something for it so when the tide get really low. It will be sitting on the cradle and not on its side, off of the ground. At high tide, it will be submerged, so you can come and go, and at low tide, is till be exosed. I make one for my boat in a weekend that i used to keep in the salt water down in tampa bay last winter when the tide on the canal got really low. It worked great, and i never had any problems with rust, i used mild steel, then when i was finsihted, i had it powder coated, after everything, it cost me about a grand to build, including the price of steel, powder coating, and all the other misc. parts. Good luck.