Welcome Ray (& wife),
We have a 2010 Laredo 5th wheel, and have been very happy with it. It's our 2nd Keystone.
I agree, 500-600 lbs is a fairly low estimate of cargo/supplies for 2 adults.
You may already know this, but... the hitch weight "listings" are for dry/unloaded hitch weights (& without options). And, as Jim suggested - using a *percentage* of a 5th wheel's GVWR is a more realistic 'estimate' of the loaded pin/hitch weight, when trying to match truck & trailer (on paper). We've always used '20%' for planning purposes.
In response to your question & comment: "can we get by with the 2500HD model?"; and "'wishing' that some knowledgable person would say that 3/4 ton would be okay..."
Wellll... what about a 'yes & no' blanket statement opinion from a Chevy owner??
Yes, some of the Laredo's may fall within the 2500 capacities/ratings; but no, probably not the ones that you're considering!
All kidding aside - there's a few Laredo owners here, so if you have any questions, we'll try to answer... without joking around! Again, welcome to the forum & good luck with your decision(s).
Terri, the Chevy co-pilot [& DH Kevin]