Rod Taylor and Sam Elliot played Travis in Darker Than Amber and The Empty Copper Sea.  Neither actor succeeded.

Why?

Fro one reason Travis is 6’4”, and having a shorter actor just does not make it . ( As this is being written there is a strong rumor that DiCaprio will be the next film Travis.)

If he were alive and at a right age Sterling Hayden would have fit the bill perfectly.  He was 6’5” and had a strong sailing background. 

Read his book: The Wanderer and you know what the water meant to him.  Very much JDM and Travis.

Oh yeah, one more thing: (from Wikipedia) 

As OSS agent John Hamilton, his World War II service included running guns through German lines to the Yugoslav partisans and parachuting into fascist Croatia. Hayden, who also participated in the Naples-Foggia campaign and established air crew rescue teams in enemy-occupied territory, became a first lieutenant on September 13, 1944, and a captain on February 14, 1945. He won the Silver Star (for gallantry in action in the Balkans and Mediterranean; "Lt. Hamilton displayed great courage in making hazardous sea voyages in enemy-infested waters and reconnaissance through enemy-held areas"), a Bronze Arrowhead device for parachuting behind enemy lines, and a commendation from Yugoslavia's Marshal Tito. He left active duty on December 24, 1945.[9]

Now, how much more would one want to qualify an actor, and real life hero,  to play Travis in the movies??

an early publicity still

From his autobiography, Wanderer, published in 1963.

    * To be truly challenging, a voyage, like a life, must rest on a firm foundation of financial unrest. Otherwise, you are doomed to a routine traverse, the kind known to yachtsmen who play with their boats at sea... cruising, it is called. Voyaging belongs to seamen, and to the wanderers of the world who cannot, or will not, fit in. If you are contemplating a voyage and you have the means, abandon the venture until your fortunes change. Only then will you know what the sea is all about. "I've always wanted to sail to the south seas, but I can't afford it." What these men can't afford is not to go. They are enmeshed in the cancerous discipline of security. And in the worship of security we fling our lives beneath the wheels of routine - and before we know it our lives are gone. What does a man need - really need? A few pounds of food each day, heat and shelter, six feet to lie down in - and some form of working activity that will yield a sense of accomplishment. That's all - in the material sense, and we know it. But we are brainwashed by our economic system until we end up in a tomb beneath a pyramid of time payments, mortgages, preposterous gadgetry, playthings that divert our attention for the sheer idiocy of the charade. The years thunder by, the dreams of youth grow dim where they lie caked in dust on the shelves of patience. Before we know it, the tomb is sealed. Where, then, lies the answer? In choice. Which shall it be: bankruptcy of purse or bankruptcy of life?