Lifespan not sure, depends on conditions.
Just rep[laced the high pressure piglet on a 5 year old h320 as it started leaking at the fitting. The rubber had lost its elasticity and seemed to have shrunk inside the fitting collar. Did not inspect the low pressure hose as the pressure test indicated the leak had been corrected. I would be more concerned on the low pressure side with chaffing of the hose especially with the gimballed stove. I always work under the motto that if it is not broken do not fix it. I test the system periodically for leaks. Shut the tank valve and observe the pressure gauge; if there is no drop in pressure within three minutes the system is not considered to be leaking. Your nose will usually let you know of a leak before the test. The high pressure side carries 140+ PSI but is contained in a locker vented to the outside. By contrast the low pressure side which goes inside the boat only carries 0.5 PSI. With a hose rated for 350 PSI the incidence of failure is almost nill.