Payload on used truck?? -- can't weigh beforehand

only real way to run either one of those campers and not exceed the tire capability is to upgrade the wheels and tires to commercial 19.5s (245/70R19.5s)for around $3500. I did that after a blow out and near roll on my 2003 F350 CC Longbed 4x4. Needless to say years later I upgraded to a Dually 4x4 and I'm glad I did as it handles the load so much better than my old SRW