You can successfully set up on the Swamp shore, but it takes a bit of doing.

1. Launch your boat at the shore at top speed.
2. Jump off, kill everything there.
3. Drop a Campfire, Workbench, or any other spawn-preventing item.
4. Run out of spawn distance.

This will prevent things from spawning near your boat both because you're too far away, and also because spawn-blocking items there are preventing them. Being too far away is important to keep things from spawning along the perimeter of your campfire/etc. and wandering to the boat.

I did this when I needed some extra Iron after mining out my main Swamp biome. I was obviously at a point where nothing in the Swamp was a major threat to me.

Just pray to Odin's beard you don't shore your boat next to an Abomination.