thanks, appreciate all the good suggestions, now just gotta measure a roof rack to see how much clearance i have, or at least SEE a bronco before i buy the light.They may not be legal to use "on" road, and therefore you may not want them to come on with the reverse lights.
I imagine you will be moving at under 10 mph, so distance isn't a thing. You just need something bright enough to see 25 - 35 feet behind you. I'd choose a single Hella Valufit S1500. It's a little pricey at almost $40.00, but Hella makes very good quality lights.
Also, you could mount it to your boat trailer and have it wired to the reverse light.