I've seen people towing three axle toy haulers with SRW trucks - IMHO, stupid is as stupid does. That said, you can pull anything you want with your truck, just don't have an accident. We're quite pleased with towing our 38' 5er with a dually. No problems with weight, cross winds, etc. Yes, it can be slightly problematic finding parking spaces when doing the tourist thing, but it hasn't been all that difficult in five years and now 45 states. (I drove Glacier's Going to the Sun Highway in both directions with it six weeks ago!)
Since you're thinking about a 30', I'd say you could go either way (unless you're planning on hauling a lot of rocks). 5ers that size usually aren't over 15k GVW and you can adjust pin weight by distributing cargo (if the fresh water tank is at the rear, fill it up).