t's a mistake to consider all campers to be the same. I don't agree they are designed to leak
True.
My '97 5th wheel trailer roof is 31'10" long and has never leaked and have never replaced all the sealant.
I'm old school...if it doesn't leak don't create one. I do a twice a year inspection looking for hairline cracks in the sealant or open sealant cracks/sealant lifting/damage to the membrane/cracked or broken roof fixtures and jacks.
I have no idea what the OEM sealant was but its done a good job. The few places I've had to add a bit of self leveling Dicor and replace sealant on one side of the skylite that debonded. No leak
Sealant is the 2nd line of defence against a leak. First line line is the grey putty tape (butyl tape) installed between the fixture/jack and the roof.
Pay close attention to the rear and especially the forward cap joint where it joins to the roof membrane.