upside and DOWNSIDE of PEX on a boat

This photo is of the short section of pipe
"T eed off" from the main cold water line to the water heater. The center piece is the check valve to prevent the hot water from expanding back into the cold water. A wealth of information! Before I get into some boring details, let me say that the tubing is cheap (1/2" 100ft $28). It is great for long runs under the sole and through floors, but it is a pain in the ass in tight areas with complicated piping. If I had it to do over I would do the runs from the tanks, and the runs to the head, ONLY, and then use braided tubing and hose clamps for the rest.
First, notice the specialized crimping tool. If you want to do PEX you have to have this tool, a tubing cutter, and another tool to remove the collar that fastens the PEX at each joint. A whole set of tools (close to $125) that you have to carry on your boat instead of a screw driver to tighten a hose clamp!!!!!!!! The crimper is in the vice because it is very hard to hold the hose with the collar sliding around, and clamp the collar at the same time. If the collar is not in the correct location, which you are guessing at because you can't see it, then you make a bad crimp, which has to be cut off with a hacksaw, grinder, or specialized tool (pain in the ass). However, after several frustrating hit or miss tries, I developed a couple of techniques. 1) I realized if the crimp tool is held in a vise then visibility for positioning is not an issue, and one hand is freed up. This method, however, depends on the idea that the short segment you are working on can be built outside the line and then inserted (not always possible). There is an array of PEX fittings available at home depot. But are they available in the middle of cruising nowhere? Anytime you are connecting PEX to conventional pipe (like on the water heater) you must screw on a PEX adaptor fitting. So since the other end of this section is a T you are , pardon the pun, screwed the way this section is built - the wrong fitting on the left. However if replaced with a pivot fitting like shown on either side of the "H" in last photo it will work. Sorry for all the detail.
Another technique, when you can't build the section with the tool in a vise, is to VERY lightly do a precrimp before putting the collar on the tubing. Then it will stay in position while you crimp.
There is another brand of connector and adaptors that just push on instead of being crimped. They don't require specialized tools. They are more expensive, but I think I would have been better off with them. Overall, except for the long runs, I would not use PEX again in a boat because installing requires space that is not really available on a boat. Nor am I excited about a carrying specialized set of tools. Over time, if repairs are needed, I will do them with braided hose and hose clamps, and my primitive screw driver. Complicated systems ensure complicated repairs! Lesson learned.