If you are backpacking in the wilderness, on a cruise, or are anywhere else where there is no Sunday Mass, you have no obligation to attend Mass. Therefore, you do not need a dispensation. The Catholic Church does not demand the impossible.
And no, you not need to refrain from strenuous outdoor activities, and instead stay home, sit in your recliner, drink beer and watch tv all weekend just to attend Mass on Sunday.
I challenge anyone to name a parish that offers any activity for adults more strenuous than chair sitting. What parish even bothers to offer wilderness trips? Or, any other type of physical activity? Or, is the typical Catholic parish just for wimps?
Also, if it is so important to attend Sunday Mass, why do the clergy refuse to put an end to liturgical abuse?
Bottom Line: No Mass, No obligation, No dispensation needed.