Can't help on the decal question, but I believe thats pretty normal for RVs. Might need some Aerospace 303 to protect the decals.
As far as roof, its SuperFlex from Alpha Systems. I use Dicor sealant and it works fine. Just wipe down the old stuff with alcohol and caulk over it. Could use Eternabond tape if you choose too. I usually clean the old stuff off to make it fairly level, then tape it up. Then come back and Dicor the edges for sanity sake.
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