I think the "buy camper first" were addressed towards potential for buying SRW
Once you have dually with heavy suspension, you never have to worry about too much camper.
I bought my dually with utility body as those sell much cheaper than all those fancy trucks with electric seats.
If you can use utility body with camper, that makes great combo, but in my case utilty body floor was 5" above the frame and I had to shim 4" to clear camper sides above the boxes.
That brought AC on my Fletwood to 13-4" level and I did not like to be that high.