In that case, NO WORRIES!
I built a set of angle-iron brackets made from 3/16th" 3" angle steel that I bolted to only one side of the chassis frame then flat-towed my Samurai 1300 miles (2092 Km) to Zuwharrie 2009 (western Missouri to North Carolina) and back. You would be suprised how tough that frame/chassis is.
Lots of folks over here have mounted aftermarket bumpers using only the inside or outside face of the chassis as mounting points.
I have heard stories of folks who had their bumpers ripped off the frame from some sort of brainless attempt to winch out but I have NEVER actually seen proof of it in person or on the Internet.
To be safe, you can fab (or buy - two-third down this page
http://www.zuksoffroad.com/ZOR-Front-Prefab-bumper-and-Options_p_41.html is a spacer style heavy-duty mount kit) a frame spacer so that your tow points are connected to both sides of the chassis frame.
BTW, that is my Zuk in the picture - and it has the spacer kit exactly as described above and by JDK's post on it.
I would worry less about the strength of the chassis frame and more about following the flat towing procedures. I severely wore down a pair of front tyres by forgetting to unlock the steering column...
I hope that this helps!