Miami to Islamorada has no hills except the Card Sound bridge if you go that way. You are probably fine if you don't go super fast on TPK or 1 to Key Largo.
In the 80s I pulled my 20 Bertram I/O (super heavy) with a Bronco II a few times. Discovered that it was too light to get up ramps w/o 4wd unless I had a lot of junk in the back seat (not enough traction even w good tires). I also got really surprised when it wouldn't activate the surge brakes when it just started raining because the Bronco II didn't weigh enough with wet/oily pavement. Got pushed through an intersection in Stuart.
Bought a K5 4WD after that.
20SC is much lighter but be ready - just in case.