If it was me of I was planning only to go a few blocks, why go thru all the hassle of inflating/deflating, etc, you want to just park the bike, lock it up, jump in the boat and go.
This means a scupper cart or cart, that you can stow on the boat, and maybe that second bar that you showed, that attaches to the bike frame, If it was me I would just leave that arm on the bike all the time.
When we are camping we tow our TI to the water with either our bike, or with our scooter (if we have the scooter along). We wind thru the campground, down to the nearest launch or beach and away we go. We just lock the bike to the nearest tree. The scooter we of course just park in a regular parking space.
Our boat is a little bigger, and we designed our regular trailer to be able to be broke down, to be used as a launching hand cart, or as a trailer (double duty).
Once thing to note, is my trailer has wheel bearings and regular tires, so it is very easy to roll.
We also have scupper carts for the boat, but the boat is kinda heavy, and the scupper carts don't have wheel bearings. If you can find a strap on cart with as large hardish wheels as possible (like bicycle tires) with wheel bearings it will be much easier to pull with a bike.
On our boat with the Hobie traxII cart, (with the grey inflatable tires), it's kind of bear to roll the boat across a large parking lot, even if it's paved. Also I doubt you could go more than a couple mph (walking speed) pulling on a standard scupper cart, might be hard to go that slow with a bike.
Keep in mind you will have a really wide turning radius, I ran mine off the road a few times biking thru the winding campground roads via the brail method.

Of course it's way easier with the scooter when we have that along:

Many campers at the places we stay at also have golf carts, we don't own one so we use this to roam around the campgrounds with.

Hope this helps
FE