Speaking of roofs...
Substrates and camper construction will vary, but I will always advocate for a liquid applied silicone roof coating if adhesion isnt an issue.
This is a place where there really is no such thing as overkill. Redundant sealing against roof moisture/leaks is key.
I use GacoRoof. Its a single part silicone that you can touch up, re-coat, etc.
Many silicones once cured has trouble bonding even to itself, not Gaco
As an example.... take this "solar tube" dome I used on ours for a sky-light.
Our camper exterior surface is marine ply, epoxy coated and painted with a single stage alkyd enamel.
Bedded in a layer of clear silicone caulk, pre-drilled and fastened with stainless wood screws, then overcoated with a few coats of GacoRoof.
After the first coat.... it goes on thick
Similar method applied to wire glands on the roof for solar cables.
No silicone used for adhesive, the roof coating already installed acts as a gasket when the gland is fastened down.
Then over-coat with more Gaco.
Same goes for roof attached tabs like solar panel brackets.
Fastened down with stainless wood screws to existing silicone roof coating, then overcoated with Gaco