Rain gutter mounts and rack size

How wide does a roof rack need to be to use the different rain gutter mounts?

Like:
Kargo Master
Surco
etc

if its a surco, it has a mounting kit that mounts to the factory roof rack side rails. You could get a Surco that is narrower than the gutter mounts, just make sure the cross bar supports on the bottom of the rack are as wide as the Jeep so you can gutter mount it. My buddy mounted a Surco that was narrower than the Jeep and just had the crossbars sticking outta the side of the rack.

My Garvin Wilderness mounted to the gutter mounts and the rack was the same width as the Jeep (from gutter mount to gutter mount), but it was a heavy mother and was kinda overkill for carrying only a spare and some lights

IMO, you would be better off going with a rack that mounts to your factory roof rack rails. No matter what the rack manufacturer says, rain gutter mounts will eventually start to rust under the clamps, and in all honesty, the rain gutters, IMO mind you, aren't that strong to begin with. I'm not sure what year you have or what you were thinking of spending, but Kevin's is worth a look. http://kevinsjeepparts.com/roof_rack.html

I'm wondering because there is a 40x60 surco for sale in my area. I'd like to have the basket go the full lenth of the jeep, so that only gives me a 40" wide base to work with.

Can you get longer cross bar supports to go with a smaller rack? I have a 40x50 inch surco that i need to get mounted to the rain gutters of my cherokee(do not have the factory roof rack).

That's kinda what I'm wondering.

Maybe if you use a Surco and instead of attaching the rack to the gutter mounts, run steel support beams from mount to mout and mount the rack to the beams.