I use a solution similar to Larry's with the difference in that I like to use silicone hose because I find it to be more resilient, thus more effective.
As regards the pump noise, the pump itself probably isn't that noisy, it's the piping that's transmitting the noise throughout the boat. The piping is filled with water, and we all know how well sound travels through water. The straighter the line, the more direct the transmission of the vibration set up by the concussion of the diaphragm action. That's why you hear it clearly in the other end of the boat.
If you can mix up the direction close to the source, it will help in diminishing the transmission. Use as flexible a hose as you can close to the pump, keep it long enough to make a full circle loop, and don't attach it directly to a solid surface. Both inlet/outlet. I've used 3/4" braided washing machine hoses; pretty robust, easy to fit, suitable for potable water, readily available in varying lengths, and large enough not to create a pressure drop problem. The loop will help dissipate the straight-line transmission, the flexible hose will convert the straight line pulses from the length to the circumference, e.g. the hose diameter will absorb some of the pulsing. If you're using PEX, it's probably amplifying the noise, you need to attenuate it close to the source.
There are commercially available equipment mounting vibration isolators that aren't terribly expensive. They're made in almost any configuration you could imagine. I use the small ones for small motors/pumps. The silicone ones are very "squishy" and provide lots of attenuation. I used them to mount the A/C unit located under our berth. Pretty amazing the reduction in sound from just those little isolators. My watermaker membrane was transmitting a huge amount of vibration into the mounting structure, a few small isolators knocked the vibration down from annoying as hell to barely discernable. Well worth the effort to implement. One tip- match the rating of the isolator as closely as possible to the weight of the equipment. Too heavy and it's not going to be effective. It needs to be able to flex to do its job.