We stayed on Gustavo's boat for 2 magical nights.
It was a great experience.
The location is amazing, you are close to all the main attractions in Belém (especially the famous Pastéis de Belém!).
Gustavo is a very nice guy, super helpful, very open minded and generous. He's the perfect host.
There are free parking spots everywhere nearby.
Just one little thing: keep in mind, that the boat rocks a little bit and the toilets are a few meters away.
We would totally recommend this place, how often can you say you stayed in Lisbon in a boat :) it's a once in a lifetime experience.