I towed with predecessors to the Express, a 1996 1500 and a 1993 G20, both 2WD conversion vans. The "96 did really well and the '93 was adequate. Both had fuel injected 350 and weighed about 6,000 lbs but 96 was Vortech and it was noticably stronger. Both were rated to tow approx 5500 to 6000 lbs. I pulled a 8x20 Pace enclosed trailer with ITA RX7 and quite a bit of spares, parts, tires, etc. I estimate loaded trailer weighed 6000 lbs. The vans drive and ride very nicely and I camped in them at the track, saving on motel bills. Vans have a lot more room inside that SUV's too. MPG was about 8 but I'd guess with the lighter open trailer around 12 MPG. I now have a 2004 Express that is a 6cyl 4.3L and I have towed a few trailers with it but it's only rated at 4,000 lbs so it would be fine with your open trailer but the enclosed trailers I've pulled with it were a bit too much. I can tow 2000 lbs with the V6 and hardly notice that anything is there. The Trailering Guide for Chevy Trucks which you can get at a Chevy dealer shows the Express with 5000 V8 rated to tow at about 5500 lbs, the 5.7 at 6100 with 3.42 axle, 6100 with 3.73 axle and 7900 with4.10 axle. The 8100 V8 is in the 7,000-10,000 range depending on axle ration. Just get a good equalizer hitch with sway control even though you might not need them. I highly recommend full size conversion vans for towing. The 3.73 rear axle works really well and I'd strongly recomment it. The 3.42 would probably work OK; it's my 2004 has. Changing rear axle ratios seems to cause complicaitons in the computer vehicles we have today. A transmission cooler is good to have and can be added at reasonable cost if the van you buy doesn't have one. I'd try to get a V8 even for the open trailer you described but the smaller one would probably do fine. My V6 gets about 18mpg empty while the V8's both were in the 15-16 range empty.
Good luck and you can often find some real values.